monograph on radiation physics … on radiation physics practical’s for medical physics students...

MONOGRAPH ON

RADIATION PHYSICS

PRACTICALS

S.Sathiyan

Monograph on Radiation Physics Practical’s for Medical Physics Students by: Dr.S.Sathiyan

Version1.0 (November, 2014) Page ii / 118

MONOGRAPH ON

RADIATION PHYSICS

PRACTICALS (for Medical Physics Students)

2014

S. Sathiyan., Ph.D

Department of Radiation Physics

Kidwai Memorial Institute of Oncology

Dr. M.H. Marigowda Road

Bangalore - 560029


Version1.0 (November, 2014) Page iii / 118

FOREWORD

It is my pleasure to write foreword note for „Monograph on Radiation Physics

Practicals‟ (for Medical Physics Students). This Practical Manual contains in depth

procedure to carry out 40 practicals. Each procedure is explained with brief theoretical

introduction followed by the method to carry out the experiment. Also it includes the

tabular columns and statistical analysis to represent and analyze the results. The

experiments included cover the Telecobalt, Linear Accelerator and Brachytherapy

facilities. The critical analysis of clinical Radiotherapy treatment Planning and

evaluation are also presented for commonly used treatment sites. Few experiments are

aimed at familiarizing the students with Radiation layout plans and shielding

calculations of Diagnostic Radiology, Nuclear Medicine, and Radiotherapy facilities.

The procedures indicated for calibration of different equipments is well presented with

easy understanding. The experiments related to radiation survey of diagnostic and

therapeutic facilities are quite informative. The author has put his time and effort in

bringing out the first of its kind monograph in our country to help the Medical Physics

fraternity. I am sure this monograph will be very useful for post graduate and post P.G

Diploma Students and teachers.

Dr. M. Ravikumar

Professor & Head

President - AMPI



Dr. M. H. Marigowda Road

Bangalore – 560 029


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PREFACE

Medical Physicists are playing an important role in the use of ionizing radiation in

medicine. The application of radiation in medicine includes diagnosis and treatment of

patients. The steady increase in cancer burden and the availability of many sophisticated

facilities require more qualified Medical Physicists. The medical physicists should have

thorough knowledge about physical aspects of radiation and its clinical implications. In

India, 19 Institutions are conducting post graduate Medical Physics course.

In Kidwai Memorial Institute of Oncology, Bangalore, a year ago, the M.Sc Radiation

Physics course was started. The experiment and practicals are part of the curriculum for

M.Sc course. The students should maintain the practical records. The Medical Physics

practical guide was not available for the students. This practical manual is prepared to

provide the guidances to the students and teachers. Monograph on Radiation Physics

Practicals contains 40 practicals. It is classified as Telecobalt, Linear Accelerator,

Brachytherapy, Treatment Planning, Layout planning and Radiation safety, Diagnostic

Radiology, Nuclear Medicine, and calibration of equipments. Monograph on Radiation

Physics practicals will provide guidance for students and teachers.

I acknowledge Dr. R. Ravichandran, Dr. M. Ravikumar, Dr. Challapalli Srinivas,

Mr. Henry Fenlay Godson and Dr. B. Shweatha for their valuable contribution in

making this practical manual.

S.Sathiyan

Assoc. Professor



Bangalore - 560029

Mob: +91 9845429525

Ph (Res): +91 80 26560352

Ph (O): +91 80 26094050

Email: [email protected]


Version1.0 (November, 2014) Page v / 118

Release of Monograph

in Inaugural function of AMPICON2014

on 20th

November 2014at Loni, Maharastra, INDIA


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CONTENTS

Telecobalt

1. Determination of absolute dose for telecobalt beam using IAEA TRS-398 protocol

2. Estimation of transmission factor for wedges, shielding trays and blocks of telecobalt machine

3. Evaluation of HVT and verification of inverse square law for the telecobalt source

4. Measurement of central axis depth dose in solid phantom for cobalt-60 beam

5. Quality Assurance procedure for telecobalt unit

Linear Accelerator

6. Measurement of absolute dose for high energy photon beams using IAEA TRS-398 protocol

7. Determination of absolute dose for high energy electron beams using IAEA TRS-398 protocol

8. Determination of virtual SSD for electron beam energy

9. Quality Assurance procedure for High Energy Linear Accelerator

Brachytherapy

10. Manual intracavitary brachytherapy calculation using Sievert integral method.

11. Manual afterloading intracavitary brachytherapy calculation using 2D treatment planning system

12. Determination of reference air kerma rate for Ir-192 brachytherapy source

13. Quality Assurance procedure for HDR brachytherapy unit

Treatment Planning and Evaluation

14. Treatment time calculations and monitor unit estimations using various treatment techniques

15. Manual isodose plotting for simple field arrangements

16. Manual calculation for an irregular field using Clarkson method

17. Computerized treatment planning for 3D conformal therapy

18. Computerized Treatment Planning for Intensity Modulated Radiotherapy Technique

19. Computerized treatment planning for HDR Intracavitary brachytherapy

20. Computerized treatment planning for HDR interstitial implant brachytherapy

21. Verification of Intensity Modulated Radiotherapy plan using absolute dosimetry

22. Verification of Intensity Modulated Radiotherapy plan using 2D dosimetry

23. Quality Assurance procedure for Dynamic Multi-leaf Collimator

24. Determination of dynamic leaf spacing for dynamic MLC fields

Layout Planning and Radiation Safety

25. Installation planning of Telecobalt therapy

26. Installation planning of high energy linear accelerator

27. Installation planning of High Dose Rate brachytherapy

28. Radiation Protection Survey of Telecoblat Machine

29. Radiation Protection Survey of High Energy Linear Accelerator

30. Radiation Protection Survey of Low Dose Rate Manual afterloading brachytherapy facility

31. Radiation Protection Survey of High Dose Rate Remote afterloding brachytherapy facility

Diagnostic Radiology 32. Installation planning of Diagnostic X-ray unit

33. Installation planning of Diagnostic CT scanner

34. Radiation protection survey of diagnostic X-ray Installation


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Nuclear Medicine 35. Installation planning of Nuclear Medicine High dose Therapy

36. Installation planning of PET-CT scanner

37. Radiation protection survey at Nuclear Medicine facility

Calibration of Instruments 38. Cross calibration of beam therapy dosimeter

39. Calibration of survey meter using Cs-137 source

Regulatory Aspects

40. Procedural aspects of transport of Radioactive Material used for Teletherpay and Brachytherapy


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1. Determination of absolute dose for telecobalt beam using IAEA TRS-398

protocol

a) AIM

i) To determine the absolute dose of telecobalt beam using TRS-398 protocol.

ii) To find out the shutter timer error.

b) REQUISITES Farmer type ionization chamber, Electrometer, Barometer, Thermometer, Phantom (water/slab)

c) THEORY

The aim of radiotherapy is to deliver the tumor with an accuracy of ±5%. In order to achieve this

absolute dose measurements are carried out in the water or water equivalent phantom with an

accuracy of ±2%. To determine absorbed dose to water, the chambers are provided with

calibration factor (ND,w,) by the secondary standard calibration laboratory traceable to Primary

standard laboratory.

Reference condition: The reference conditions for the determination of absorbed dose to water

in 60

Co gamma ray beam are given below.

Table 1: Reference conditions for the determination of absorbed dose to water in

60Co gamma ray

beams

Influence quantity Reference value or reference characteristics

Phantom material Water

Chamber Cylindrical or parallel plate

Measurement depth, Zref 5 g/cm2 (or 10 g/cm

2)

Reference point of the chamber

For cylindrical chambers, on the central axis at the

centre of the cavity volume. For parallel plate

chambers, on the inner surface of the window at its

centre

Position of the reference point of the

chamber

For cylindrical and plane-parallel chambers, at the

measurement depth Zref

SSD or SCD 80 cm or 100 cm

Field size 10 cm x 10 cm

Determination of absorbed dose under reference condition:

The absorbed dose to water at the reference depth Zref in water, in the absence of chamber is

Dw = M ND,w ------------(1)

where M is the meter reading of the dosimeter with the reference point of the chamber

positioned at Zref, in accordance with the reference conditions given in the above table and

corrected for the influence quantities such as temperature and pressure, electrometer calibration,

polarity effect and ion recombination.

M = Ml KTP Kpol KsKelec ------------------ (2)



where Ml is the uncorrected dosimeter reading (at V1 polarity) nC/min or rdg/min.

Pressure and temperature correction factor KTP

where P0 and T0 are the reference pressure and temperature, P and T are the measured pressure

and temperature.

Electrometer calibration factor Kelec.

The value of Kelec is generally 1 if the electrometer is calibrated along with the chamber.

Polarity correction factor KPol

where M+ is the meter reading (nC) for the polarity +V1, M- is the meter reading for the polarity

–V1.

Ion recombination correction (Two voltage method) factor Ks

where V1/ V2 is the voltage ratio, M1/M2 is the ratio of meter reading for voltage V1 & V2.

Absorbed dose to water at Zmax:

Clinical dosimetry calculations are often referred to the depth of dose maximum Zmax. To

determine the absorbed dose at Zmax the user should use the central axis percentage depth dose

(PDD) data for SSD set-up and tissue maximum ratios (TMR) for SAD set-up.

Timer Error: The timer error can influence the meter reading (Ml) significantly. Timer error

should be taken into account.

where R1 is integrated reading at time t, R2 is the integrated reading at two shot exposure for the

same time t.

d) PROCEDURE

Place the water/slab phantom (dimension 30x30x30 cm3) on the treatment table. Set the gantry

& collimator angle 0. Maintain the water phantom surface at 80 cm and chamber depth at 5 cm

from the surface. Measure the pressure and temperature, before starting the experiment and at the

end of the experiment, take the average value for P & T correction. Perform the open field



irradiation for 5 min for warm-up and residual ion collection. Set 10x10 cm2 field size for

absolute measurement. Collect the meter readings for the exposure time„t‟.

Figure: experimental setup for absorbed dose measurement

e) OBSERVATIONS

Electrometer: Chamber:

SSD: 80 cm Field size: 10 cm x 10 cm Depth of measurement: 5 cm

Absorbed dose to water calibration factor ND,W = Gy/C or Gy/meter reading

Reference conditions for calibration: Po: _______ mbar To: ________ °C

Average environmental conditions during measurement: P: ______ mbar T: ________ °C

Warm-up for 5 min

Irradiation time, t = minutes

S.No Meter Reading (nC)

For +V1= For -V1= For +V2=

1

2

3

4

5

Avg Ml=



Dw,z,ref = M ND,w cGy/min

M = Ml KTP Kpol KsKelec

Ml= ________, KTP=__________, V1/V2 =__________, M1/M2=________

Kpol=_______, Ks=__________, Kelec =___________

Dw,Zmax = Dw,z,ref / 0.788 cGy/min

Percentage Variation with respect to reference value:

Shutter timer error

f) RESULTS

i) The measured output for telecoblat unit is ___________cGy/min as on (date)

ii) The measured shutter error is ________sec. The treatment time has to be corrected for +/-

____sec.

iii) The deviation of measured output with respect to reference value is ______%



2. Estimation of transmission factor for wedges, shielding trays and

blocks of telecobalt Machine

a) AIM

To determine wedge, block, and shielding tray transmission factors used in the telecobalt

machine.

a) REQUISITES

Farmer type ionization chamber, Electrometer, slab phantom, wedges, shielding tray and blocks,

etc,.

b) THEORY Wedge: Wedge filters or absorbing blocks are placed in the path of a beam to modify its isodose

distribution. The most commonly used beam-modifying device is a wedge filter. The wedge-

shaped absorber that causes a progressive decrease in the intensity across the beam, resulting in a

tilt of the isodose curves from their normal positions. As shown in Figure, the isodose curves are

tilted toward the thin end, and the degree of tilt depends on the slope of the wedge filter.

Figure: Isodose curve for wedge field

The wedge is usually made of a dense material, such as lead or steel, which can be inserted in the

beam at a specified distance from the source. This distance is arranged such that the wedge tray

is always at a distance of at least 15 cm from the skin surface, so as to avoid destroying the skin-

sparing effect of the megavoltage beam.

Wedge Angle: Wedge angle is the angle between the 50% isodose curve and the normal to the

central axis.



Wedge transmission factor: The presence of a wedge filter decreases the output of the machine,

which must be taken into account in treatment calculations. This effect is characterized by the

wedge transmission factor (or simply wedge factor), defined as the ratio of doses with and

without the wedge, at a point in phantom along the central axis of the beam. This factor should

be measured in phantom at a suitable depth beyond the depth of maximum dose (e.g., 5 cm or10

cm). The output at Dmax must be corrected using wedge factor.

Shielding Blocks: Shielding blocks are most commonly made of lead, tungsten. The thickness of

lead required to provide adequate protection of the shielded areas depends on the beam quality

and the allowed transmission through the block. A primary beam transmission of 5% through the

block is considered acceptable for most clinical situations.

Block transmission factor: It is defined as ratio of doses with and without transmission block.

Tray transmission factor: The trays are used to mount the blocks at a particular distance from

the source. The presence of a blocking tray decreases the output of the machine, which must be

taken into account in treatment calculations. The tray transmission factor is defined as the ratio

of doses with and without blocking tray.

c) PROCEDURE

Measurement of wedge transmission factor: Position the gantry and collimator at 0. Place

the ionization chamber at 5 cm depth in water/slab phantom. For a given wedge angle & field

size, find out the meter reading with and without wedge. The ratio of reading is the wedge factor

at 5 cm depth. Find out the wedge factor at dmax depth using PDD. Also find out the wedge factor

in non-wedge direction.

Measurement of tray transmission factor: Position the gantry and collimator at 0. Place the

ionization chamber at 5 cm depth in water/slab phantom. For a given shielding tray, find out the

meter reading with and without shielding tray for the field sizes 10 cm x 10 cm & 30 cm x 30

cm. The ratio of reading is the shielding tray factor at 5 cm depth. Find out the shielding factor at

dmax depth using PDD.

Block transmission factor: Position the gantry and collimator at 0. Place the ionization

chamber at 5 cm depth in water/slab phantom. For field size 10cm x 10cm, find out the meter

reading with and without block. Place the effective volume of chamber exactly at the midpoint of

the block. The ratio of reading is the block transmission factor at 5 cm depth. Find out the block

transmission factor at dmax depth using PDD.



d) OBSERVATIONS

Electrometer: Chamber: SSD: Depth of measurement:

Wedge Factor

Find out the wedge factor at dmax (Measurement at 5 cm depth & convert to dmax)

Wedge angle Field size MR with Wedge MR without

wedge

Wedge Factor

Tray Factor Find out the tray factor at dmax (Measurement at 5 cm depth & convert to dmax)

Tray Type Field size MR with Tray MR without Tray Tray Factor

Block transmission factor

Find out the block transmission factor at dmax (Measurement at 5 cm depth & convert to dmax)

Block Type Field size MR with block MR without

block

Block

transmission

factor

e) RESULTS

i) The measured wedge transmission factor for _________ wedge is _________

ii) The measured tray transmission factor for _________tray is ________

iii) The measured block transmission factor for the _______ block is ________.



3. Evaluation of HVT and verification of inverse square law for the

telecobalt source

a) AIM

i) To evaluate half value thickness (HVT) for a telecobalt source, assuming the conditions of

narrow beam geometry.

ii) To study the effect of inverse square using telecobalt machine.

b) REQUISITES

Farmer type ionization chamber, Electrometer, slab phantom, wedges, shielding tray and blocks,

etc,.

c) THEORY

Half value thickness:

As gamma radiation passes through matter, it undergoes absorption by interaction with atoms of

absorbing material, principally by photoelectric effect, Compton effect and by pair production.

The result is a decrease in the intensity of the radiation with the distance transverse through the

absorbing material. The decrease in intensity of an incident beam of gamma radiation is

exponential in form, given by

I=I0 e-µx

loge I/I0 = -µx

loge I0/I = µx ---------(1)

where I0 is the intensity of incident beam, I is the intensity after traversing a distance x through

the material and µ is the linear attenuation coefficient. A useful concept regarding absorption of

gamma ray is half value thickness (HVT) or half value layer (HVL). This is defined as the

thickness of the absorber required to decrease the intensity of the beam to one half of the initial

intensity. Thus, after the gamma ray has passed through a half value thickness of the absorber,

the intensity of the beam I is equal to I0/2. Rearranging equation (1) and substitute I0/2 for I.

loge 2 = µx1/2

log10 2 = µx1/2

x1/2 = HVL = 0.693 / µ.

Inverse square law:

The exposure at any point from a source of X or gamma rays varies inversely as the square of the

distance of the point from the source. Larger the distance, lesser will be the radiation dose.

Intensity (I) α 1/d2

I1/I2 = d22/d1

2

I2 =

I1 d1

2/d2

2

where I1 is the intensity at d1 distance, I2 is the intensity at d2 distance.



d) PROCEDURE

Determination HVT: Position the gantry at 90 or 270. Place the farmer type ionization

chamber with buildup cap at 100 cm distance from the source, note down the meter reading for 1

min exposure. Place each 1cm perspex absorber in between source and detector (approximately

at 60cm distance from the source), note down the meter reading, repeat the experiment for each

1cm absorber placed in the beam. Proceed the experiment for minimum of 2 HVT values. Plot a

graph of x versus loge I0/I.

Inverse square measurement: Position the gantry at 90 or 270. Place the farmer type

ionization chamber with buildup cap at different distances like 60, 70, 80, 90, 100, 110 & 120 cm

distances, note down the meter reading for 1 min exposure. Maintain the narrow beam geometry

by selecting the smallest field size and shield blocks. Plot a graph of distance versus intensity.

Figure 1: experimental setup for inverse square measurement

Figure 2: experimental setup for HVL measurement



e) OBSERVATIONS

Electrometer: Chamber: SSD:

Field size:

HVT measurement:

S.No Absorber thickness

(cm)

Meter Reading (nC)

1 2 3 Average

0

Inverse square measurement:

S.No Distance (cm) Meter Reading (nC)

1 60 1 2 3 Average

2 70

3 80

4 90

5 100

6 110

7 120

f) RESULTS

i) The half value thickness obtained from the graph is ________

ii) The effect of inverse square law is shown in the graph.



4. Measurement of central axis depth dose in solid phantom for cobalt-

60 beam

a) AIM To measure depth dose in solid phantom for cobalt -60 beam along the central axis of the beam

for different field size.

b) REQUIREMENTS

Secondary standard dosimeter, solid phantom, telecobalt machine. etc,.

c) THEORY

The quantity central axis depth dose (or simply percentage depth dose) may be defined as the

quotient, expressed as a percentage, of the absorbed dose at any depth „d‟ to the absorbed dose at

a fixed reference depth „d0‟, along the central axis of the beam.

Percentage depth dose (P)

Figure: Percentage depth dose (Dd/Dd0)

The percentage depth dose at a point depends on beam energy, depth, source to surface distance

and beam area.

d) PROCEDURE

Position the gantry and collimator at 0. Depth dose depends on the depth „d‟. Provide the

sufficient backscatter for the measurement (5 to 10 cm). Place the ionization chamber in the slab



phantom, which is having 0.5 cm grove dmax (d0) buildup. Position the phantom top always at 80

cm SSD. Fix the field size 10cm x 10 cm, adjust the chamber position at centre of the cross

wires. Find out the meter reading for set time„t‟ at dmax depth. Add each known phantom

thickness (say 1cm) on the top of the chamber and lower the treatment couch for same SSD.

Repeat exposure for at least 10 measurement depths. Find out the percentage depth dose for

atlest 3 field sizes (5cm x 5cm, 15cm x 15cm, 20cm x 20cm) and 5 depths (3, 5, 10, 15, and 20

cms).

e) OBSERVATIONS

Dose dependency on depth ‘d’

Source to surface distance (SSD):________

Field size:____________

Meter reading at d0:_____________

S.No Depth (d)

cm

Meter reading at depth ‘d’ % depth dose

(Dd/Dd0)x100 1 2 3 Avg

Dose dependency on field size

S.No Field

size

cm x cm

Meter reading at depth ‘d0’ Meter reading at depth ‘d’ %

depth

dose 1 2 3 Avg 1 2 3 Avg

f) RESULTS

i) A graph of depth versus percentage depth dose is plotted.

ii) A graph of field size versus percentage depth dose is plotted.



5. Quality Assurance procedure for telecobalt unit

a) AIM To perform the Quality Assurance test for telecobalt unit

b) REQUIREMENTS

Field size template, Graph sheet, Therapy verification film, front pointer, slab phantom, etc.

c) THEORY

Quality Assurance is defined as a process through which actual performance of the equipment is

measured and compared with the existing standard or reference value (base line value) and

actions necessary to keep or regain uniformity with these standards are taken.

Necessity of Quality Assurance (QA): To ensure the therapy unit performance according to

specification and that unit is safe to use for both patient and staff. To guarantee the dose delivery,

to minimize the chance of accidents, to prevent errors, to minimize the machine down time and

promote preventive maintenance procedures.

QA of Telecobalt unit: QA of telecobalt unit concern with three different types of testing i)

Type approval, ii) Performance/Acceptance testing, iii) QA or periodic QA test.

i) The type approval is given by the regulatory body of country (AERB in India) for the

equipment to be used.

ii) Performance/Acceptance test is done by user at the time of commissioning of the equipment.

i) Periodic QA test is done on regular basis like weekly, monthly and annually to ensure the

function of the equipment within the tolerance limit.

QA test can be grouped into three categories viz., Electrical, mechanical and radiation test.

d) PROCEDURE

Electrical tests: Testing the proper functioning of various interlocks, source „ON‟ condition

display, control console display and their functions, CCTV display. All the tests should be

performed every day before starting the treatment. All the tests are qualitative measurements to

prevent any emergency situation.

Mechanical & Radiation tests: Perform the QA test as per procedure and record the values in

the observation

e) OBSERVATIONS

Mechanical tests:

Physical Characteristics

Couch Minimum couch level above floor : cm

Horizontal Motion : from cm to cm

Vertical Motion : from cm to cm

Lateral motion : From to cm

Rotational motion : from deg to deg



Couch locks :

Provided? : Yes / No

Working? : Yes / No

Shift in optical field due to vertical motion from min. to max. position: (Tolerance: 2 mm)

Shift in optical field due to rotational motion from -90 deg to 90 deg: (Tolerance: 2 mm) Couch material:

Collimator Rotational angle : from to Field sizes available

Lower jaw : from cm to cm

Upper jaw : from cm to cm

Distance from isocentre : cm

Optical beam & collimator axis

Coincidence : mm

Parallelism of the jaws

Lower jaw :

Upper jaw : (Tolerance: 1.0)

Orthogonality of the adjacent jaws :

Symmetry of jaws : mm (Tolerance : < 1mm)

Optical field overlap

0 and 180 : mm

90 and 270 : mm (Tolerance: 1.0 mm)

Gantry

3.1.3.1

RPM (.1 to 1) tests : (Tolerance : 1%)

3.1.3.2

Isocentre : mm dia (Tolerance : < 4.0 mm dia.

sphere)

Read – out Accuracy SSD or SAD verification : Stated (cm) Measured

(cm)

Mechanical front pointer :

Optical distance indicator :

Laser beam indicator :

(Tolerance: < + 1.5 mm.)



Field size (Fs) definition

Set optical Field size(cmXcm)

Measured optical field size (cmXcm) at 00 Gantry Position Tolerance

+x -x +y -y

5x5 For F≤ 10x10, ≤ 1.0mm 10x10

15x15

20x20

25x25 For F> 10x10, ≤ 2.0mm 30x30

35x35

40x40

Radiation Checks: Congruence Between Optical and Radiation Fields: Place a paper packed therapy verification film with proper build-up thickness at treatment

distance. Set 10cm x10cm optical field on the film surface. Place angled lead wires at the

corners of the optical field and also on the lines defining the cross- wires (but outside the field).

Expose the film so as to get an optical density of nearly 1.

Film used :

Exposure : cGy

Set Field : cm x cm

Radiation Field : (measured 50 % width in two orthogonal directions).

L to R : cm.

G to F : cm.

Tolerance: < 2 mm.

f) RESULTS

The parameters were checked in telecobalt unit through the Quality Assurance procedure. The

measured values are within the tolerance limit.



6. Measurement of absolute dose for high energy photon beams using IAEA

TRS-398 protocol

a) AIM To determine the absolute dose from high energy photon beams using TRS-398 protocol

b) REQUISITES

Farmer type ionization chamber, Electrometer, Barometer, Thermometer, Phantom (water/slab),

etc,.

c) THEORY

The aim of radiotherapy is to deliver a dose with an accuracy ±5% to the tumor. In order to

achieve this absolute dose measurements are carried out in the water or water equivalent

phantom with an accuracy of ±2%. For user chamber, the absorbed dose to water calibration

factors (ND,w,Q0) are provided by the calibration laboratory (Primary standard/Secondary

standard Labs) with traceable to Primary/Secondary standard. ND,w,Q0 is the absorbed dose to

water calibration factor for the reference beam quality Q0 (Telecoblat beam).

Beam Quality Specification: For high energy photons produced by clinical accelerators the

beam quality Q is specified by the tissue phantom ratio TPR. This is the ratio of the absorbed

doses at depths of 20 and 10 cm in a water phantom, measured with a constant SCD of 100 cm

and a field size of 10 cm X 10 cm at the plane of the chamber. The most important characteristic

of the beam quality index is TPR , it‟s independence of the electron contamination in the incident

beam.

Table 1: Reference conditions for the determination of photon beam quality (TPR20,10)



Chamber Cylindrical or parallel plate

Measurement depths 20 g/cm2 and 10 g/cm

2



centre of the cavity volume. For parallel plate

chambers, on the inner surface of the window at its

centre


chamber

For cylindrical and plane-parallel chambers, at the

measurement depths

SCD 100 cm


Reference conditions: The reference condition for determination of absorbed dose to water in

high energy photon beam is shown in table 2.



Table 2: Reference conditions for the determination of absorbed dose to water in high energy

photon beams



Chamber Cylindrical

Measurement depth Zref For TPR20,10 < 0.7, 10 g/cm2 (or 5 g/cm

2)

For TPR20,10 0.7, 10 g/cm2


On the central axis at the centre of the cavity volume


chamber

At the measurement depth Zref

SCD 100 cm


Determination of absorbed dose to water under reference condition:

The absorbed dose to water at the reference depth Zref in water for photon beam of quality Q

and in the absence of the chamber is

Dw,Q =MQ ND,w,Q0 KQ,Q0 --------------(1)

where MQ is the reading of the dosimeter with the reference point of the chamber positioned at

Zref in accordance with the reference conditions and corrected for the influence quantities such as

temperature and pressure, electrometer calibration, polarity effect and ion recombination. ND,w,Q0

is the calibration factor in terms of absorbed dose to water for the dosimeter at the reference

quality Q0. KQ,Q0 is a chamber specific factor which corrects for the difference between the

reference beam quality Q0 and actual beam quality Q (Beam quality correction factor).

MQ = Ml KTP Kpol KsKelec -------------------(2) [Ref. equation (2) from practical 1 ]

Absorbed dose at Zmax: Clinical dosimetry calculations are often referred to the depth of dose

maximum Zmax. To determine the absorbed dose at Zmax the user should use the central axis

percentage depth dose (PDD) data for SSD set-up and tissue maximum ratios (TMR) for SAD

set-up.

d) PROCEDURE

Measurement of beam quality:

The experimental set-up for measuring TPR is shown in Fig.1. The reference conditions of

measurements are given in Table 1. Although the definition of TPR20,10 is strictly made in terms

of ratios of absorbed dose, the use of ionization ratios provides an acceptable accuracy owing to

the slow variation with depth of water/air stopping-power ratios and the assumed constancy of

perturbation factors beyond the depth of dose maximum. Place the water phantom surface at 100

cm SCD with 0 gantry and collimator angle. Position the chamber at 10 cm depth from the

surface (SSD = 90cm). Repeat the measurement with chamber positioned at 20 cm depth (SSD =

80 cm).



Figure 1: Experimental setup for TPR20,10 measurement

Measurement of absorbed dose to water: Perform the open field irradiation for 500 MU for

warm-up and residual ion collection. Place the water phantom surface at 100 cm SSD with 0

gantry and collimator angle. Position the chamber at 10 cm depth in phantom. Set the 10x10 cm2

field size for absolute measurement; Collect the meter readings for the 100 MU setting. Measure

the pressure and temperature, before starting the experiment and at the end of the experiment,

take the average value for P & T correction. Repeat the measurement for different polarizing

voltage and dual voltage.

e) OBSERVATIONS


SSD: 100cm Field size: 10 cm x 10 cm Depth of measurement: 10 cm

Absorbed dose to water calibration factor ND,w = Gy/C or Gy/meter reading



Warm-up for 500MU



Figure 2: experimental setup for absorbed dose measurement

Irradiation for 100MU



1

2

3

4

5

Avg Ml=

Dw,z,ref = M ND,w KQ,Q0 cGy/MU


Ml= ________, KTP=__________, V1/V2 =__________, M1/M2=________

Kpol=_______, Ks=__________, Kelec =___________

Dw,Zmax = Dw,z,ref / PDD cGy/min

percentage variation with respect to reference value:

f) RESULTS i) The measured output of 6MV/18MV photon beam is ___________cGy/MU

ii) The deviation of measured output with respect to the reference value is ______%



7. Determination of absolute dose for high energy electron beams using

IAEA TRS-398 protocol

a) AIM To determine absolute dose from high energy electron beams using TRS-398 protocol.

b) REQUISITES

Parallel plate ionization chamber, Electrometer, Barometer, Thermometer, water Phantom, etc,.

c) THEORY

The aim of radiotherapy is to deliver dose to the tumor with an accuracy of ±5%. In order to

achieve this, absolute dose measurements are carried out in the water or water equivalent

phantom with an accuracy of ±2%. For user chamber, the absorbed dose to water calibration

factors (ND,w,Q0) are provided by the calibration laboratory (Primary standard/Secondary

standard Labs) with traceable to Primary/Secondary standard. ND,w,Q0 is the absorbed dose to

water calibration factor for the reference beam quality Q0 (Telecoblat beam).

Beam Quality Specification: For electron beams the beam quality index is the half-value depth

in water R50. This is the depth in water (in g/cm) at which the absorbed dose is 50% of its value at

the absorbed dose maximum, measured with a constant SSD of 100 cm and a field size at the

phantom surface of at least 10 cm × 10 cm for R50 ≤ 7 g/cm2

(E≤ 16 MeV) and at least 20 cm ×

20 cm for R50 7 g/cm2

(E 16 MeV).

Table 1: The reference conditions for the determination of electron beam quality


Phantom material For R50 4 g/ cm2 , Water

For R50˂ 4 g/ cm2 , Water or plastic

Chamber type For R50 4 g/ cm2 , Plane parallel or Cylindrical

For R50 ˂ 4 g/ cm2, Plane parallel


For plane parallel, chambers, on the inner surface of

the window at its centre.


centre of the cavity volume


chamber

For plane parallel, chambers, at the point of interest.

For cylindrical chambers, 0.5 rcyl deeper than the point

of interest.

SCD 100 cm

Field size at phantom surface For R50 ≤ 7 g/ cm2 , at least 10 cm x 10 cm

For R50 ˃ 7 g/ cm2 , at least 20 cm x 20 cm



Reference conditions: The reference condition for determination of absorbed dose to water in

electron beams is shown in table 2.

Table 2: Reference conditions for the determination of absorbed dose in electron beams


Phantom material For R50 4 g/ cm2 , Water

For R50˂ 4 g/ cm2 , Water or plastic

Chamber type For R50 4 g/ cm2 , Plane parallel or Cylindrical

For R50 ˂ 4 g/ cm2, Plane parallel

Measurement depth Zref 0.6 R50 – 0.1 g/cm2


For plane parallel, chambers, on the inner surface of

the window at its centre.


centre of the cavity volume


chamber

For plane parallel, chambers, at Zref

For cylindrical chambers, 0.5 rcyl deeper than Zref

SCD 100 cm

Field size at phantom surface 10 cm x 10 cm or that used for normalization of

output factors, whichever is larger

Determination of absorbed dose in water under reference condition

The absorbed dose to water at the reference depth zref in water, in an electron beam of quality Q

and in the absence of the chamber, is

Dw,Q =MQ ND,w,Q0 KQ,Q0 --------------(1)

where MQ is the reading of the dosimeter with the reference point of the chamber positioned at

Zref in accordance with the reference conditions and corrected for the influence quantities

temperature and pressure, electrometer calibration, polarity effect and ion recombination. ND,w,Q0

is the calibration factor in terms of absorbed dose to water for the dosimeter at the reference

beam quality Q0. KQ,Q0 is a chamber specific factor which corrects for the difference between the

reference beam quality Q0 and actual beam quality Q (Beam quality correction factor).

MQ = Ml KTP Kpol KsKelec -------------------(4) [Ref. equation (2) from practical 1]

Absorbed dose at zmax: Clinical normalization most often takes place at the depth of the dose

maximum zmax. which, does not always coincide with zref. To determine the absorbed dose at zmax

the user should measured the central axis depth dose distribution and convert the absorbed dose

at zref to that at zmax.



d) PROCEDURE

Measurement of absorbed dose to water: Place the water phantom surface at 100 cm SSD with

0 gantry and collimator angle. Select the reference field applicator either 10x10 or 15x15.

Position the parallel plate chamber at zref depth in water phantom. Measure the pressure and

temperature, before starting the experiment and at the end of experiment; take the average value

for P & T correction. Perform open field irradiation with 500 MU for warm-up and residual ion

collection. Collect the meter reading for the 100 MU setting. Determine the absolute dose for

given electron energies.

Figure: experimental setup for absorbed dose measurement

e) OBSERVATIONS


SSD: 100cm Applicator: 10x10 or 15x15 Depth of measurement (zref) : cm






Warm-up for 500MU

Irradiation for 100 MU Energy:



1

2

3

4

5

Avg Ml=

Dw,z,ref = M ND,w KQ,Q0 cGy/MU


Ml= ________, KTP=__________, V1/V2 =__________, M1/M2=________

Kpol=_______, Ks=__________, Kelec =___________

Dw,Zmax = Dw,z,ref / PDD cGy/min

Percentage Variation with respect to reference value:

f) RESULTS

i) The measured output of 6MeV/9MeV/-------electron beam is ___________cGy/MU

ii) The variation of measured output with respect to reference value is ______%



8. Determination of virtual SSD for electron beam energy

a) AIM

To determine the virtual source to surface distance for electron beam energies

b) REQUIREMENTS

Parallel plate ionization chamber, Electrometer, solid/water phantom, etc.,

c) THEORY Unlike an x-ray beam, an electron beam does not emanate from a physical source in the

accelerator head. A pencil electron beam, after passing through the vacuum window of the

accelerator, bending magnetic field, scattering foils, monitor chambers, and the intervening air

column, is spread into a broad beam that appears to diverge from a point. This point is called the

virtual source, which may be defined as an intersection point of the back projections along the

most probable directions of electron motion at the patient surface. This is illustrated in Figure

Figure 1: Definition of virtual point source of an electron beam

The virtual source point is found by the back projection of the 50% width of the beam profiles

obtained at different distances. A broad beam (≥20 × 20 cm) is used for these measurements. The

use of virtual SSD does not give accurate inverse square law correction for output at extended

SSDs under all clinical conditions. Measurements have shown that the virtual SSD gives correct

inverse square law factor only for large field sizes. For small field sizes, the inverse square law

correction underestimates the change in output with virtual SSD. This deviation from the inverse

square law is caused by an additional decrease in output because of a loss of side-scatter

equilibrium in air and in phantom that is significant for small field sizes and low electron

energies. Thus, the use of the virtual SSD to predict dose variation with distance requires



correction factors, in addition to the inverse square law factor, as a function of field size and

energy.

An alternative method of correcting dose output for the air gap between the electron collimator

and the patient is to determine effective SSD, which gives the correct inverse square law

relationship for the change in output with distance. Khan et al have recommended a method that

simulates as closely as possible to the clinical situation. In this method, doses are measured in a

phantom at the depth of maximum dose (dm), with the phantom first in contact with the cone or

at the standard SSD (zero gap) and then at various distances, up to about 20 cm from the cone

end. Suppose f = effective SSD, I0 = dose with zero gap, and Ig = dose with gap g between the

standard SSD point and the phantom surface. Then, if electrons obey inverse square law:

-----------(1) or --------------(2)

By plotting √I0/Ig as a function of gap g, a straight line is obtained, the slope of which is:.

f =1/slope - dm as shown in figure 2.

Figure 2: Determination of effective source to surface distance

Although the effective SSD is obtained by making measurements at the depth dm, its value does

not change significantly with the depth of measurement. However, the effective SSD does

change with energy and field size, especially for small field sizes and low energies.

d) PROCEDURE

1) Place the parallel plate ionization chamber at dmax for given energy and applicator in slab

phantom as shown in figure 3.

2) Measure the dose for 100 cm SSD setup (no gap)

3) Repeat the measurement for increasing SSD by 2 cm interval up to 20 cm gap.



4) Repeat the measurement for given energies and applicator

5) Plot a graph between gaps (g) versus √I0/Ig.

6) obtain the slope value and calculate the effective SSD

Figure 3: experimental setup for determination of virtual SSD

e) OBSERVATIONS


Depth of measurement (zref) : cm

Warm-up for 500MU

Irradiation for 100MU Energy: Applicator:

SSD

(cm)

Meter Reading (nC) Avg.

1 2 3

100

102

104

106

120



Energy:

Distance (cm) Effective SSD (cm)

6x6 10x10 15x15 20x20 25x25

100

102

104

120

f) RESULTS

1) A table of effective SSDs as a function of energy and field size is shown.

2) Necessary clinical situations are met.



9. Quality Assurance procedure for High Energy Linear Accelerator

a) AIM To perform the Quality Assurance test for high energy linear accelerator.

b) REQUIREMENTS

Field size template, Graph sheet, Therapy verification film, pointer, slab phantom, etc.

c) THEORY








QA of Linear Accelerator: QA of linear accelerator concern with three different types of

testing i) Type approval, ii) Performance/Acceptance testing, iii) QA or periodic QA test.

i) The type approval is given by the regulatory body of country (AERB in India) for the

equipment to be used.

ii) Performance/Acceptance test is done by user at the time of commissioning of the equipment.

8. Periodic QA test is done on the regular basis like weekly, monthly and annually to ensure the

function of the equipment within the tolerance limit.

QA test can be grouped into three categories viz., Electrical, mechanical and radiation test.

d) PROCEDURE

Electrical tests: Testing the proper functioning of various interlocks, Beam „ON‟ condition

display, control console display and their functions, CCTV display. All the tests should be

performed every day before starting the treatment. All the tests are qualitative measurement to

prevent the emergency situation.

Mechanical & Radiation tests: Perform the QA test as per procedure and record the values in

the observation

e) OBSERVATIONS

Mechanical Tests

Physical characteristics

Couch

Level above floor :

cm

Horizontal motion : from cm to cm Vertical motion : from cm to cm



Lateral motion : from cm to cm Rotational motion : from deg to deg Speed : max. cm/sec Limit: 5cm/sec

: min. cm/sec Limit.: 1cm/sec

Collimator

Angular scale test : Tolerance 0.5 Distance from isocentre : cm

Optical & collimator axes : mm Tolerance: 1mm coincidence

Conventional jaws - Symmetric and asymmetric motion

Jaw size

Lower jaw : from cm to

cm Upper jaw : from cm to cm

Parallelism of the jaws : Lower : Upper : Tolerance: 1°

Orthogonality of the adjacent jaws: Tolerance: 90° ± 1° Symmetry of jaws : Asymmetric jaw over travel distance: cm

Multileaf collimator (MLC) jaws

MLC type : X – Jaws, Y – Jaws, Tertiary

(tick) No. of leaf pairs : Leaf width at isocentre : mm Leaf thickness : cm Leaf over-travel distance : cm Inter-leaf spacing : mm Intra-leaf spacing : mm Speed of leaves : cm /sec

Abutting of leaves on and :

off the field central axis Reproducibility of leaf : mm Tolerance: 1 mm

positions Interlocks for leaf : Yes / No Tolerance: functional Jaw position interlocks : Yes / No Tolerance: functional Alignment of MLC axes and : Yes / No Tolerance: 1 mm

secondary collimator axes Collimator centering

Use a field size of 10 cm x 10 cm and place a graph paper at isocentre with collimator at 0°. Record the

maximum deviations of the upper and lower jaws for combinations of gantry and collimator angles at 0°.

Repeat the observations for MLC leaf ends and sides.

Maximum difference (a) between jaws : , mm (b) leaves : , mm Tolerance: 2 mm

Correspondence between : Acceptable / Not acceptable

MLC irregular fields & shapes and BEV

target cross-section



Tolerance: 2 mm

Gantry

Tolerance: 0 1%

Rotation speed (.1 to 1 RPM) :

Isocentre

(a) Mechanical

Collimator rotation isocentre :

mm Gantry rotation isocentre : mm Couch rotation isocentre : mm Coincidence of collimator, gantry :

and couch axes with isocentre mm

Radiation

Radiation isocentre :

mm

Coincidence between radiation and :

mechanical isocentre

mm

Tolerance: ≤ 2 mm diameter sphere

Readout accuracy

Stated Measured

SSD / SAD verification :

cm ; cm Mechanical front pointer :

value verification

Tolerance: 2 mm

Multi-leaf collimator (MLC) For MLC, use the manufacturer provided leaf position table in auto-cycle mode. Record

the leaf positions observed on the graph paper and verify that the measured leaf position

matches w i t h the specifications wi th in t h e tolerance limits. Tabulate the

observations for evaluation and record.

Tolerance: 1 mm



Symmetric Jaws and Square Fields

Set optical field size, cm x cm

Measured optical field size, cm x cm at Gantry Position

+X -X -Y +Y

Tolerance

5 x 5 For Fs ≤

10x10

± 1 mm

10 x 10

15 x 15

20 x 20 & 25 x 25

30 x 30 For Fs >

10 cm x10 cm

≤ 2 mm

35 x 35 40 x 40

Radiation Checks

Photon Beam Characteristics Congruence between optical and radiation fields The congruence between optical and radiation fields must be assessed at the depth of the reference

plane - which is usually at SSD + d or with the reference plane placed at the isocentre of the accelerator -

for square fields of 10 cm x 10 cm at 0° gantry angle for each nominal photon energy (MV).

The separation between optical field edge and the 50% isodose line shall not exceed 2 mm.

Light Field and Radiation Field Congruence L – R vs Field Size (each photon energy) Place film at 100 cm SFD on a leveled surface. Set fields

using specified collimator settings. Measure 50% edge and distance between corresponding cross-wires.

Insert graticule tray. Deliver 70 MU (no build-up). Set 10 cm x 10 cm field, give 10 MU. Compare the

congruence between set optical and radiation fields.

f) RESULTS

Various parameters were checked in Linear Accelerator through the Quality Assurance

procedure. The measured values are within the tolerance limit.



10. Manual intracavitary Brachytherapy calculation using Sievert

Integral method

a) AIM

To calculate the prescribed dose rate at reference point in intracavitary brachytherapy patient

using Sievert Integral calculation method.

b) REQUIREMENTS

Sievert integral table, source details, patient orthogonal film, etc.,

c) THEORY

Radiation therapy using discrete source kept in close proximity to the lesion of interest is

referred to as brachytherapy. The main advantage of this technique is that, it delivers localized

high dose to the tumor volume. Depending on the types of application & technique it can be

classified as surface mould, interstitial brachytherapy and intracavitary bracytherapy.

Intracavitary brachytherapy: Sources are inserted into natural body cavities using applicator

in defined geometry. It is generally referred for treatment of gynaecological tumor. The sources

used are Cs-137, Co-60 & Ir-192 in the form of pellets, seeds, tubes, wire and miniature

cylinders.

Dosimetry in intracavitary Bracytherapy: The sources are placed in the cervix applicator, the

applicator consists of central uterine tandem, which contains 2-3 tube sources. Two lateral

capsules called ovoids contain one tube source each and are separated by rubber spacer. These

are placed in the vagina.

Dose specification is recommended based on the Manchester system. It includes point A, point

B, Bladder and Rectum doses. The point A is defined at the location where uterine vessels

crosses the ureter.

Figure 1: Original definition of points A and B, according to the Manchester system



Measurement of dose rate: Dose rate at any point around the linear Barchytherapy source can

be found using Sievert Integral

Figure 2: Geometry of linear source

Exposure rate at point P is

-----------(1)

----------(2)

where A- Activity of source (mCi)

Γ – exposure rate constant (3.32 R cm2/hr/mCi for Cs-137)

L – active length of source

µ- linear attenuation coefficient

secƟ = 1/cosƟ

t- thickness of sheathing material

y-height of the point from source plane

Dose rate at a point P

Dp = I (x,y) x f ----------------(3)

where f – Roentgen to rad conversion factor (0.957)



[Note: use TAR(r) or f-factor for dose conversion; TAR(r = ((AP+BP)/2)]

d) PROCEDURE

1) Obtain the manual brachytherapy patient orthogonal films.

2) Find out magnification factor

3) Mark the source and point A positons

4) De-magnify and find out x,y,z co-ordinates for each source and point A

5) Transfer the co-ordinate to graph sheet.

6) Find out dose rate at point A from each source.

7) Calculate the treatment time for the prescribed dose.

e) OBSERVATIONS & CALCULATIONS

From figure 2 y2 = AP

2 – AO

2 ------------(4)

= AP2 – (L+w)

2

y

2 = BP

2 – w

2 --------------(5)

AP2 = (x1-x)

2 + (y1-y)

2 + (z1-z)

2

BP2 = (x2-x)

2 + (y2-y)

2 + (z2-z)

2

By solving equation (4) & (5) find out „w‟, from equation (5) & find out „y‟

tanƟ1 = w/y; tanƟ2 = (L+w)/y

Find out Ɵ1 & Ɵ2

Using equation (2) and Sievert integral table find out the integral values. Using equations (3)

find out the dose rate at point „P‟.

Source

No.

Source coordinate Source

strength

(mCi)

L

(cm)

y w Ɵ1 Ɵ2 Exposure

rate at

point p

Dose

rate

(cGy/hr)

x1 y1 z1 x2 y2 z2

f) RESULTS

i) The total dose rate at point A is _______

ii) Total treatment time is _____________



11. Manual afterloading intracavitary Brachytherapy calculation using

2D Treatment Planning System

a) AIM

To calculate the prescribed dose rate to the reference point in intracavitary brachytherapy patient

using treatment planning system.

b) REQUIREMENTS

Source details, patient orthogonal film, treatment planning system (TPS), viewing box, etc.,

c) THEORY

Radiation therapy using discrete source kept in close proximity to the lesion of interest is

referred as brachytherapy. The main advantage of this technique is it delivers localized high dose

to the tumor volume. Depending on the types of application & technique it can be classified as

surface mould, interstitial brachytherapy and intracavitary bracytherapy.

Intracavitary brachytherapy: Sources are inserted into natural body cavities using applicator

in defined geometry. It generally referred for treatment of gynaecological tumor. The sources

used are CS-137, Co-60 & Ir-192 in the form of pellets, seeds, tubes, wires and miniature

cylinders. Dosimetry in intracavitary Bracytherapy: The sources are placed in the cervix

applicator, the applicator consists of central utrine tandem contains 2-3 tube sources

Two lateral capsules called ovoids contain one tube source each and separated by rubber spacer.

These are placed in the vagina.

Dose specification is recommended based on Manchester system. It includes point A, point B,

Bladder and Rectum doses. The point A is defined at the location where uterine vessels crosses

the ureter.

Figure 1: Original definition of points A and B, according to the Manchester system



d) PROCEDURE

1) Obtain the manual brachytherapy patient orthogonal films.

2) Find out the magnification factor

3) Mark source and reference point positions in Lateral film and transfer the coodiante to AP

film

4) Feed the x,y,z coordiantes of reference points and source

5) Perform the calculation in TPS

6) Find out point A, point B, Bladder and Rectum dose rates

7) Calculate total Bladder dose, total rectal dose and treament time.

e) OBSERVATION

AP magnification factor:____________ Lateral magnification factor:_____________

Source/Reference

points

Source coordinate Source strength (mCi)

x1 y1 z1 x2 y2 z2

Point A dose rate:________ Bladder dose rate:________ Total Bladder dose:_______

Point B dose rate:________ Rectum dose rate:________ Total Rectum dose:________

f) RESULTS

i) The calculated dose rate to point A is ____________

ii) The calculated treatment time is ___________



12. Determination of reference air kerma rate for Ir-192 Brachythreapy

source

a) AIM

i) To determine the source position accuracy of Ir-192 source in HDR brachytherapy unit.

ii) To determine the reference air kerma rate for Ir-192 HDR brachytherapy source.

b) REQUIREMENTS

Well chamber, Electrometer, HDR brachytherapy machine, Thermometer, Barometer, etc.,

c) THEORY

Routine calibration of brachytherapy sources is usually carried out with a “re-entrant”-type ion

chamber in which the walls of the chamber surround the source, approximating a 4π

measurement geometry. The well type chamber for brachytherapy source calibrations should be

of the type designed especially for radiotherapy applications, capable of measuring the reference

air kerma rate of both LDR and HDR sources. It is recommended that only well type chambers

which are open to the atmosphere be used. If the chamber is sealed and the pressure of the gas is

at a higher level than the ambient atmospheric pressure, it may develop a problem of slow

leakage of the gas. In this case, a change in the calibration factor would result. Chambers open to

the atmosphere need correction for temperature and pressure since the calibration factor is based

upon a density of air corresponding to standard ambient conditions, usually 20C and 1013.2

mbar.

Calibration point inside the well type chamber (measurement of sensitive position)

The calibration point is with the source at the position of maximum response. With the source

positioned at this point, the uncertainty in the reference air kerma rate determination, due to

positional uncertainty, is minimized. This position is dependent on the source type and must be

determined prior to the calibration. Measurements are performed at different positions of the

source along the axis of the chamber by adjusting the dwell position of the source.

Measurement corrections

Recombination correction, Kion may be determined using the two-voltage technique. If the ratio

of the voltage used in this technique is exactly 2 (e.g. if 150V and 300V are used, as is often the

case with well type chambers) then the recombination correction can be determined as

1/Kion = 4/3 – [Q1/(3.Q2)]

where Q1 is the charge collected at the higher voltage (i.e. at 300V) and Q2 is the charge

collected at the lower voltage (i.e. 150V).

Reference air kerma rate (RAKR)

Reference air kerma rate is



RAKR = Mu. NRAKR.(1/Kion)

where Mu is meter reading corrected for ambient condition, NRAKR is air kerma rate calibration

factor in Gy.m2 hr

-1 A

-1.

d) PROCEDURE

Find out the source position accuracy using graph sheet and gafchromic film.

Position the source holder inside the well chamber. Find out the maximum sensitivity position of

the well chamber from the bottom by adjusting the dwell position of the source. Plot the graph

between positions versus response. Find out the meter reading at the maximum sensitivity

position for two different voltages. Use these meter readings to find out the reference air kerma

rate.

Figure: experimental setup for RAKR measurement

e) OBSERVATIONS

Chamber: Electrometer:

Decay Factor: Step size:

Operating bias voltage:



Measurement of sensitivity position

Position Distance from the

bottom position (cm)

Response (nA)

Measurement for RAKR

Sl. No Response (nA)

for Bias Voltage (+300V)

Response (nA)

Bias Voltage (+150V)

Average Mu =

NRAKR = Gy.m2 hr

-1 A

-1

Mu = nA

Kion =

RAKR = Mu. NRAKAR.(1/Kion)

RAKR= µGy. m2 hr

-1

f) RESULTS

i) The measured source position accuracy is within _________

ii) The maximum sensitivity position is ______

iii) The measured reference air-kerma rate is ___________

iv) Reference air kerma rate quoted by the manufacturer _______________

v) Deviation from the manufacturer quoted value_____________



13. Quality Assurance procedure for HDR Brachytherapy unit

a) AIM

To perform the Quality Assurance test for Ir-192 HDR brachytherapy unit

b) REQUIREMENTS

Ir-192 HDR brachytherapy unit, well type ionization chamber and electrometer, applicators,

Guide tube, etc.,

c) THEORY








HDR Remote after Loading Brachytherapy unit: The QA procedure of HDR unit may be

broadly divided into (a) operational testing of the afterloading unit, (b) radiation safety check of

the facility, (c) checking of source calibration and transport, and (d) checking of treatment

planning software. This practical mainly focuses on operational testing of the after loading unit.

d) PROCEDURE

Perform the Quality Assurance test as per the protocol and record the observations

e) OBSERVATIONS

Treatment Unit

Make, Model & Number:

Maximum capacity of the Unit : 15Ci

Radionuclide : 192

Ir

Physical dimensions of source: Length: mm ; Dia.: mm

Total & individual activity of sources: mGy/h at 1m (mCi)

(as quoted by the supplier) : mGy/h at 1m (mCi)

QA Tests : Mechanical

1. Functioning of sensors like pressure, torque, optical : Satisfactory / No

2. Coupling between guide tube and unit - : Satisfactory / No

3. Coupling between guide tube and applicator - : Satisfactory / No

4. Coupling between drive cable and source : Satisfactory / No

5. Time taken to drive the source to "ON" position : --------- sec



6. Time taken to withdraw the source to “OFF" position : -------- sec 7. Temporal Accuracy (Tolerance: ± 1 %)

Timer error : 0.5% (Tolerance) Timer linearity : 0.5% (Tolerance) End error : 1-2sec ('or' %)(Tolerance) 8. Source guide free of kinks? : Yes/No

9. Mechanical integrity of applicators & position of shield, if any: Acceptable / Not acceptable

QA Tests : Electrical

1. Interlocks

1. Treatment Room Door(s) Working? : Yes / No

2. Guide Tube & Treatment Unit Working? : Yes / No

3. Applicator & Guide Tube Working? : Yes / No

4. Emergency stop button to interrupt the irradiation Working? : Yes / No

2. Source Safe Display

1. Treatment "OFF" indicator Working? : Yes / No

2. Treatment "ON" indicator Working? : Yes / No

3 Control Console Display

1. Treatment "OFF" indicator Working? : Yes / No

2. Treatment "ON" indicator Working? : Yes / No

3. Source ON/OFF indicator Working? : Yes / No

4. Door interlock indicator Working? : Yes / No

5. Retrieval of the source indicator Working? : Yes / No

6. Retrieval of the dummy indicator Working? : Yes / No

7. Emergency `OFF‟ switch Working? : Yes / No

8. Treatment and elapsed time display counters Working? : Yes / No

9. Multi-channel indexer function and sequence displays Working? : Yes / No

10. Back-up system(s) Provided? : Yes / No

QA Tests: Radiation

1. Positioning Accuracy and Uniformity (Tolerance: ± 1 mm)

(use autoradiograph / radiograph wherever required)

1. Coincidence between dummy and active source positions: ------ mm

2. Accuracy of source position within the applicator: ------- mm

3. Reproducibility of dummy source position: -------- mm

QA Tests: Radiation Safety

1. Gamma Zone Monitor: Working? : Yes / No

2. CCTV Working? : Yes / No

f) RESULTS

Various parameters were checked in High dose rate brachythreapy unit through the Quality

Assurance procedure. The measured values are within the tolerance limit.



14. Treatment time calculation and monitor unit estimation using

various treatment techniques

a) AIM

i) To determine the treatment time for a given patient dose prescription using both SSD and

SAD technique.

ii) To determine the Monitor Unit for a given patient dose prescription using both SSD and SAD

technique.

b) REQUIREMENTS

Dose prescription for the given patient, Output chart, calculator, etc.

c) THEORY Several methods are available for calculating the absorbed dose in patients. Two of these

methods are more common, percent depth doses and tissue-air ratios (TARs). However, there

are some limitations in these methods. For example, the dependence of percent depth dose on

source to surface distance (SSD) makes this quantity unsuitable for isocentric techniques.

Although tissue-air ratios (TARs) and scatter-air ratios (SARs) eliminate this problem, their

application to beams of energy higher than those of 60

Co has been seriously questioned as they

require measurement of dose in free space. As the beam energy increases, the size of the

chamber buildup cap for in-air measurements has to be increased and it becomes increasingly

difficult to calculate the dose in free space from such measurements. In addition, the material of

the buildup cap is usually different from that of the phantom and this introduces a bias or

uncertainty in the TAR measurements. In order to overcome the limitations of the TAR, the

concept of tissue-phantom ratio (TPR) was introduced. This quantity retains the properties of the

TAR but limits the measurements to the phantom rather than in air. A few years later, the

concept of tissue-maximum ratio (TMR) was introduced, which also limits the measurements to

the phantom. In source to axis distance (SAD) dose calculation TPR or TMR can be used.

SSD Technique (Telecobalt)

Percentage depth dose (%dd)d is a suitable quantity for calculations involving SSD techniques.

The machine outputs (OP) are usually calibrated in terms of cGy/min for the reference field size

10 x 10 at dmax depth. Output factor (OPF) depends on the field size, if wedges and trays are

used, (Wedge factor (WF) & tray factor (TF)) factors are to be taken into consideration. In the

absence of these beam modifiers, the factor is 1.

Treatment time = Given dose (cGy)

OP x OPF x WF x TF

Given dose = Tumor dose/ (%dd)d

Isocentric Technique (Telecobalt)



TMR is the quantity of choice for dosimetric calculations involving isocentric techniques. The

machine outputs (OP) are usually calibrated in terms of cGy/min for the reference field size 10

cm x 10 cm at dmax depth. Output factor (OPF) depends on the field size, if wedges and trays are

used (Wedge factor (WF) & tray factor (TF)), factors are to be taken into consideration. In the


Treatment time = Prescribed dose or Tumour dose (cGy)

OP x OPF x WF x TF x TMR x SSD factor

SSD factor = [(SSD+ dmax) / SAD]2

SSD Technique (Linear Accelerator)

Percent depth dose is a suitable quantity for calculations involving SSD techniques. Machines

are usually calibrated to deliver 1 cGy per monitor unit (MU) at the reference depth dmax, with

reference field size 10 cm × 10 cm. Sc is the collimator scatter factor, Sp is the phantom scatter

factor and Sc,p is the output factor related to the collimator field sizes, if wedges and trays are

used (Wedge factor (WF) & tray factor (TF)), factors are to be taken into consideration. In the


Monitor Unit (MU) = Given dose (cGy)

OP x Sc,p x WF x TF

Given dose = Tumor dose/ (%dd)d

Isocentric Technique (Linear Accelerator)

TMR is the quantity of choice for dosimetric calculations involving isocentric techniques.

Machines are usually calibrated to deliver 1 cGy per monitor unit (MU) at the reference depth

dmax, with reference field size 10 cm × 10 cm. Sc is the collimator scatter factor, Sp is the

phantom scatter factor and Sc,p is the output factor relate to the collimator field sizes, if wedges

and trays are used (Wedge factor (WF) & tray factor (TF)), factors are to be taken into

consideration. In the absence of these beam modifiers, the factor is 1.

Monitor Unit (MU) = Prescribed dose or Tumour dose (cGy)

OP x Sc,p x WF x TF x TMR x SSD factor

SSD factor = [(SSD+ dmax) / SAD]2



d) PROCEDURE

1) A carcinoma cervix patient has to be treated in telecobalt machine with AP/PA technique.

The prescribed dose is 45Gy in 25 fractions. AP/PA separation is 20 cm, field size 15 cm x

19 cm. Calculate the treatment time.

2) A carcinoma cervix patient has to be treated in linear accelerator using 6 MV photon beam

with four field box SAD technique. The prescribed dose is 45Gy in 25 fractions. AP/PA

separation 20 cm and lateral separation is 35 cm, AP/PA field size 15 cm x 19 cm & (RL/LL)

Lateral field size 14 cm x 19 cm. Consider 95% isodose coverage and calculate the Monitor

unit.

3) A carcinoma rectum patient has to be treated in telecobalt unit with four field box SAD

technique. The prescribed dose is 50 Gy in 25 fractions. AP/PA separation 19 cm and lateral

separation is 34 cm, AP/PA field size 15 cm x 18 cm & (RL/LL) Lateral field size 11 cm x

18cm. Consider 95% isodose coverage and calculate the treatment time.

4) A patient with Glioma has to be treated in linear accelerator machine using 6 MV photon

beam with SSD perpendicular wedge field technique. The prescribed dose is 60 Gy in 30

fractions. AP field size 8 cm x 10 cm, depth 5 cm & Lateral field size 10 cm x 10 cm, depth

3.5 cm. Use 45 physical wedge. Consider 95% isodose coverage and calculate the Monitor

unit.

i) Check the prescribed dose per fraction, depth or separation, treatment field size, energy,

treatment machine, use of shielding/ wedge, etc.

ii) Find out equivalent square field size

iii) Find out PDD or TMR

iv) Find out output, output factor (Sc,p), dose per fraction, wedge factor, tray factor

v) Calculate given dose/Tumor dose, calculate SSD factor

vi) Calculate treatment time or Monitor unit.

e) OBSERVATION & CALCULATION

Prescribed dose: Gy, Number of fractions: Separation/Depth: Field size:

Equivalent square field = 2ab/(a+b), where a- width of the field , b-length of the field

Output: , OPF= ,Sc,p = , (%dd)d= TMR= ,WF= ,TF=

SAD Factor=

Treatment time=

Monitor unit=

f) RESULTS

i) The calculated treatment time/MU for AP field is _______

ii) The calculated treatment time/MU for PA field is _______

iii) The calculated treatment time/MU for lateral field is _______



15. Manual isodose plotting for simple field arrangement

a) AIM

i) To plot a manual isodose for given AP/PA parallel oppose field plan.

ii) To plot a manual isodose for given perpendicular wedge field plan.

b) REQUIREMENTS Contour sheet, caliper, isodose charts, etc,.

c) THEORY The central axis depth dose distribution by itself is not sufficient to characterize a radiation beam

that produces a dose distribution in a three-dimensional volume. In order to represent volumetric

or planar variation in absorbed dose, distributions are depicted by means of isodose curves,

which are lines passing through points of equal dose. The curves are usually drawn at regular

intervals of absorbed dose and expressed as a percentage of the dose at a reference point. An

isodose chart for a given beam consists of a family of isodose curves usually drawn at equal

increments of percent depth dose, representing the variation in dose as a function of depth and

transverse distance from the central axis. The depth dose values of the curves are normalized

either at the point of maximum dose on the central axis or at a fixed distance along the central

axis in the irradiated medium. The charts in the first category are applicable when the patient is

treated at a constant source to surface distance (SSD) irrespective of beam direction. In the

second category, the isodose curves are normalized at a certain depth beyond the depth of

maximum dose, corresponding to the axis of rotation of an isocentric therapy unit. This type of

representation is especially useful in rotation therapy but can also be used for stationary

isocentric treatments.

Figure: Isodose curve



Combination of Radiation Fields: Treatment by a single photon beam is seldom used except in

some cases in which the tumor is superficial. For treatment of most tumors, combinations of two

or more beams are required for an acceptable distribution of dose within the tumor and the

surrounding normal tissues.

Parallel Opposed Fields: The simplest combination of two fields is a pair of fields directed

along the same axis from opposite sides of the treatment volume. The advantages of the parallel

opposed fields are the simplicity and reproducibility of setup, homogeneous dose to the tumor,

and less chance of geometric miss (compared with angled beams), given that the field size is

large enough to provide adequate lateral coverage of the tumor volume. A disadvantage is the

excessive dose to normal tissues and critical organs above and below the tumor.

Wedge field technique: By inserting appropriate wedge filters in the beam and positioning them

with the thick ends adjacent to each other, the angled field distribution can be made fairly

uniform. The dose falls off rapidly beyond the region of overlap or the “plateau” region, which is

clinically a desirable feature. There are three parameters that affect the plateau region in terms of

its depth, shape, and dose distribution: θ, Φ, and S, where θ is the wedge angle, Φ is the hinge

angle, and S is the separation. The hinge angle is the angle between the central axes of the two

beams and the separation S is the distance between the thick ends of the wedge filters as

projected on the surface.

There is an optimum relationship between the wedge angle θ and the hinge angle Φ that provides

the most uniform distribution of radiation dose in the plateau:

Ɵ = 90 - /2

d) PROCEDURE

i) Obtain the contour and target volume for carcinoma cervix and buccal mucosa patients

ii) Obtain the isodose chart for required field size

iii) Draw the isodose curve for the required plan

iv) Transfer the resultant isodose line and body structures to another contour sheet.

v) Mark the percentage of isodose lines clearly.

e) RESULTS

i) The percentage of dose covering the target volume in the AP/PA plan is ________

ii) The percentage of dose covering the target volume in the perpendicular wedge field plan is

________



16. Manual calculation for an irregular field using Clarkson method

a) AIM

To calculate the scatter component (SMR) of the irregular field using Clarkson method.

b) REQUIREMENTS

Irregular field contour (Mantle field or inverted Y), Protractor, scale, TMR table, etc,.

c) THEORY Any field other than the rectangular, square or circular field may be termed as irregular.

Irregularly shaped fields are encountered in radiation therapy when radiation-sensitive structures

are shielded from the primary beam or when the field extends beyond the irregularly shaped

patient body contour. Examples of such fields are the mantle and inverted Y fields used for the

treatment of Hodgkin's disease. Since the basic data (percent depth dose, tissue-air ratios, or

tissue-maximum ratios) are available usually for rectangular fields, methods are required to use

these data for general cases of irregularly shaped fields. One such method, originally proposed

by Clarkson and later developed by Cunningham has proved to be the most general in its

application.

Clarkson's method is based on the principle that the scattered component of the depth dose,

which depends on the field size and shape, can be calculated separately from the primary

component, which is independent of the field size and shape. A special quantity, Scatter

Maximum Ratio (SMR), is used to calculate the scattered dose.

d) PROCEDURE

Figure: Outline of mantle field in a plane perpendicular to the beam axis and at a specified

depth



An irregularly shaped field is shown in Figure. Assume this field cross section to be at depth „d‟

and perpendicular to the beam axis. Let „Q‟ be the point of calculation in the plane of the field

cross section. Radii are drawn from „Q‟ to divide the field into elementary sectors. Each sector is

characterized by its radius and can be considered as part of a circular field of that radius. If we

suppose the sector angle is 10 degrees, then the scatter contribution from this sector will be

10°/360 = 1/36 of that contributed by a circular field of that radius and centered at „Q‟. Thus, the

scatter contribution from all the sectors can be calculated and summed by considering each

sector to be a part of its own circle, the scatter-maximum ratio of which is already known and

tabulated.

Using an SMR table for circular fields, the SMR values for the sectors are calculated and then

summed to give the average scatter maximum ratio ( ) for the irregular field at point Q.

For sectors passing through a blocked area, the net SMR is determined by subtracting the scatter

contribution by the blocked part of sector. For example

net (SMR)QC = (SMR)QC - (SMR)QB + (SMR)QA

The computed is converted to an average tissue maximum ratio by the equation

= TMR(0) +

where TMR(0) is the tissue maximum ratio for 0 × 0 field; that is:

TMR(0) = e-µ(d-d

m)

where µ is the average linear attenuation coefficient for the beam and „d’ is the depth of point Q.

The percent depth dose (%dd) at Q may be calculated relative to dmax on the central axis using

equation

%dd =100 x x [(f+dm)/(f+d)]2 / BSF

where BSF is the backscatter factor for the irregular field and can be calculated by Clarkson's

method. This involves determining TMR at the depth dm on the central axis, using the field

contour or radii projected at the depth dm.

e) OBSERVATIONS

1) Obtain the irregular contour

2) Calculate the average TMR and percentage depth dose as per above procedure

f) RESULTS

i) The calculated average TMR is ________

ii) The calculated PDD is ___________



17. Computerized treatment planning for 3D conformal therapy

a) AIM

To perform the 3D conformal therapy planning for the given patient.

b) REQUIREMENTS

Treatment planning system, Dose prescription information and dose constrains, etc.,

c) THEORY

Computerized treatment planning systems (TPSs) are used in external beam radiotherapy to

generate beam shapes and dose distributions with the intent to maximize tumour control and

minimize normal tissue complications. Patient anatomy and tumour targets can be represented as

3-D models. The entire process of treatment planning involves many steps and the medical

physicist is responsible for the overall integrity of the computerized TPS to accurately and

reliably produce dose distributions and associated calculations for external beam radiotherapy.

The development of CT based computerized treatment planning, providing the ability to view

dose distributions directly superimposed upon a patient‟s axial anatomy. Successive

improvements in treatment planning hardware and software have been most notable in the

graphics, calculation and optimization aspects of current systems. Systems encompassing the

„Virtual Patient‟ are able to display beam‟s eye views (BEVs) of radiation beams and digitally

reconstructed radiographs (DRRs) for arbitrary dose distributions. Dose calculations have evolved

from simple 2-D models through 3-D models to 3-D Monte Carlo techniques, and increased

computing power continues to increase calculation speed. The entire treatment planning process

involves many steps, beginning from beam data acquisition and entry into the computerized TPS,

through patient data acquisition, to treatment plan generation and the final transfer of data to the

treatment machine.

d) PROCEDURE

i) The 3D CRT planning has to be carried out for carcinoma cervix patient using 4 field box

techniques. Prescription dose for PTV is 50 Gy in 25 fractions. Limit the dose to rectum,

bladder and femoral head doses below 80% of prescribed dose.

ii) Use 4 gantry angles 0, 180,90 and 270, if required use collimator angle.

iii) Adjust the MLC positions to the target in all fields with sufficient margin.

iv) Limit dose to critical organs using MLC.

v) Calculate the dose.

vi) Note maximum, minimum and mean dose to PTV volume.

Vii) Using DVH to find out dose coverage to 100%, 98% and 95% of the PTV volume.

vii) Make a note of critical organ doses, find out the volume which receives 50% of the dose.

viii) Find out homogeneity index and conformity index.



e) OBSERVATIONS

Patient name: Hosp.No.: RT.No.:

Prescribed dose (PTV): Fractions:

PTV doses:

D100= D95= V100= V95=

Conformity index(CI95%) = Dose to 95% of volume/Prescribed dose =

Homogeneity index (HI) = (D98% - D2%) / Prescribed dose =

Critical organ doses:

Bladder

D30cc = D10cc = D0.1cc= Mean dose=

Rectum


Lt femoral head


Rt femoral head


f) RESULTS

The 3D CRT planning was carried out for carcinoma cervix patient and the dose-volume details

were recorded.



18. Computerized Treatment Planning for Intensity Modulated

Radiotherapy Technique

a) AIM

To perform Intensity modulation radiotherapy treatment planning for given patient.

b) REQUIREMENTS

Treatment planning system, Dose prescription information and dose constraints, etc.,

c) THEORY

Computerized treatment planning systems (TPSs) are used in external beam radiotherapy to

generate beam shapes and dose distributions with the intent to maximize tumour control and

minimize normal tissue complications. Patient anatomy and tumour targets can be represented as

3-D models. The entire process of treatment planning involves many steps and the medical

physicist is responsible for the overall integrity of the computerized TPS to accurately and

reliably produce dose distributions and associated calculations for external beam radiotherapy.

The term intensity-modulated radiation therapy (IMRT) refers to a radiation therapy technique in

which non-uniform fluence is delivered to the patient from any given position of the treatment

beam to optimize the composite dose distribution. The treatment criteria for plan optimization are

specified by the planner and the optimal fluence profiles for a given set of beam directions are

determined through “inverse planning.” The fluence files thus generated are electronically

transmitted to the linear accelerator, which is computer controlled, that is, equipped with the

required software and hardware to deliver the intensity-modulated beams (IMBs) as calculated.

Multileaf collimator (MLC)–based IMRT can be delivered by two main modalities namely

segmental IMRT (step and shoot) and dynamic IMRT (sliding window). In the step-and-shoot

modality, the MLC shape remains constant while the beam is on and changes while the beam is

off and in the sliding window, each leaf pair moves continuously, unidirectionally, and with

independent speed while the beam is on. Any shape of intensity profile can be obtained by

controlling the leaf movement, subject to the mechanical constraints, such as leaf width,

maximum speed, field size, etc. imposed by the multileaf collimator (MLC) system. As leaf

motions are controlled by a computer, the IMRT technique lends itself to automated treatment

delivery eliminating the need for re-entry into the room between fields.

d) PROCEDURE

The IMRT planning has to be carried out for Glioma (Skull) patient using 7 field dynamic IMRT

technique. Prescription dose for PTV is 60 Gy in 30 fractions. Limit the dose to brainstem,

chiasm, optic nerves, eyes, lens and pituitary.

i) Enter prescribed dose and number of fraction to target volume.

ii) Place the 7 beams with equal gantry angle.

i) Perform the optimization using target volume and critical organs dose constraints.

ii) With the satisfactory dose optimization, perform the 3D dose calculation.

iii) Evaluate the dose coverage in each axial CT.



iv) Analyze the Dose-Volume Histogram (DVH).

v) Note maximum, minimum and mean dose to PTV volume.

vi) Make a note of critical organ doses, find out the volume which receives 50% of the dose.

vii) Find out homogeneity index and conformity index

e) OBSERVATIONS


Prescribed dose (PTV): Fractions:

PTV doses:

D100= D95= V100= V95=

Conformity index(CI95%) = Dose to 95% of volume/Prescribed dose =

Homogeneity index (HI) = (D98% - D2%) / Prescribed dose =


Brainstem

Maximum dose= D0.1cc= Mean dose=

Chiasm


Optic nerves


Eyes


Lens


Pituitary


f) RESULTS

The IMRT planning was carried out for Glioma patient and the dose-volume details were

recorded.



19. Computerized treatment planning for HDR Intracavitary

Brachytherapy

a) AIM To perform the 3D CRT treatment planning for intracavitary brachytherapy patient.

b) REQUIREMENTS Treatment planning system, CT scan images, Dose prescription, dose constraints etc.,

c) THEORY Radiation therapy using discrete source kept in close proximity to the region of interest is referred

to as brachytherapy. The main advantage of this technique is that it delivers localized high dose to

the tumor volume. Depending on the type of application & technique it can be classified as

surface mould, interstitial brachytherapy and intracavitary bracytherapy.

Intracavitary brachytherapy: Sources are inserted into natural body cavities using applicator in

defined geometry. It generally referred for treatment of gynaecological tumor. The sources used

are Co-60 & Ir-192 in the form of pellets, wire and miniature cylinders.

Dosimetry in intracavitary bracytherapy: The sources are placed in the cervix applicator; the

applicator consists of central uterine tandem, two lateral capsules called ovoids. These are placed

in vagina.

The CT/MRI compatible applicators and development of computer software is suitable for three

dimensional (3D) intracavitary treatment planning. Structures of interest can be contoured on 3D

images and the dose distribution can be more accurately evaluated with the help of dose-volume

histograms (DVHs).

d) PROCEDURE

1) Obtain the CT images with contour for intracavitary brachytherapy patients.

2) Run the optimaziation with dose constraints for CTV and organs at risk.

3) Adjust the isodose with dose shaper.

4) Evaluate the dose in each axial CT image and analyze DVH.

e) OBSERVATION


Prescribed dose (CTV): Fractions:

CTV doses:

D100= D90= V100= V200=


Bladder




Rectum


f) RESULTS

The 3D conformal brachytherapy planning was carried out for the intracavitary brachytherapy

patient and the doses were analyzed.



20. Computerized treatment planning for HDR interstitial implant

Brachytherapy

a) AIM

To perform the 3D CRT treatment planning for interstitial implant brachytherapy patient.

b) REQUIREMENTS Treatment planning system, CT scan images, Dose prescription, dose constrains etc.,

c) THEORY

Radiation therapy using discrete source kept in close proximity to the region of interest is referred

as brachytherapy. The main advantage of this technique is it delivers localized high dose to the

tumor volume. Depending on the type of application & technique it can be classified as surface

mould, interstitial brachytherapy and intracavitary bracytherapy.

Interstitial implant brachytherapy: when Fletcher-type ovoids cannot be accommodated. If a

tandem and ovoid or tandem and ring applicator cannot be inserted because of vaginal narrowing,

the absence of fornices, or vaginal extension of disease, interstitial implantation is preferred. Only

if this is not available, a tandem and cylinder applicator may be used. It should be realized that

use of the cylinder results in lower parametrial doses and higher bladder and rectal doses relative

to tumor, with a possible increase in complications and pelvic failures. In the treatment of cervix

cancer, the interstitial gynecologic template system has been used for patients with advanced-

stage cervical cancer. The interstitial system is applied most commonly in an attempt to increase

the dose to the region outside the standard pear-shaped isodose distribution, such as the

parametrial, paravaginal, or paraurethral regions.

Dosimetry in intracavitary bracytherapy: The GYN template is composed of many catheter

implants plus a tandem based on the Syed-Neblett gynecologic template or MUPIT template.

The CT/MRI compatible applicators and development of computer software is suitable for three

dimensional (3D) interstitial implant treatment planning. Structures of interest can be contoured

on 3D images and the dose distribution can be more accurately evaluated with the help of dose-

volume histograms (DVHs).

d) PROCEDURE

1) Obtain the CT images with contour for interstitial implant brachytherapy patients.

2) Run the optimaziation with dose constrains for CTV and oragan at risks.

3) Adjust the isodose with dose shaper.

4) Evaluate the dose in each axial CT image and analyze the DVH.



e) OBSERVATION


Prescribed dose (CTV): Fractions:

CTV doses:

D100= D90= V100= V200=


Bladder


Rectum


f) RESULTS

The 3D conformal brachytherapy planning was carried out for the interstitial implant

brachytherapy patient and the doses were analyzed.



21. Verification of Intensity Modulated Radiotherapy plan using

absolute dosimetry

a) AIM

To verify the Intensity Modulated Radiotherapy plan using absolute point dose method.

b) REQUIREMENTS

Ionization chamber, phantom, thermometer, barometer, TPS, etc,.

c) THEORY

Intensity modulated radiotherapy (IMRT) planning demands stringent quality assurance and

accurate dose determination for delivery of highly conformal dose to the patients. Generally 3-D

dose distributions obtained from a treatment planning system have to be verified by dosimetric

methods. The verification includes absolute dosimetry for all treatment fields and relative

dosimetry for each treatment portal.

The plan is acceptable for treatment only when the measured absolute dose is within 3% of the

calculated dose. If the difference between measured and calculated dose is 3% to 5%, the plan has

to be reviewed and verified. When the difference is beyond 5% the plan is unacceptable and

rejected.

d) PROCEDURE

Use 2mm axial cut CT scan images of solid water phantom with ion chamber for dose

measurement.

Using phantom image set, create the verification plan from the patient‟s plan.

Calculate the dose distribution and normalize it to isocentre, which represents the centre of ion

chamber at the depth of 5 cm from the phantom surface.

Export the plan to treatment unit through network and measure the dose, compare the same with

TPS calculated dose.

e) OBSERVATIONS

Patient Name: Hospital No.: RT Number:

Energy: Electrometer: Chamber:

SSD: 95cm SAD: 100 cm Depth of measurement: 5cm




Figure: experimental setup for point dose measurement



Warm-up for 500MU

Cumulative meter reading (M) =

Absolute dose at isocentre = M Ktp ND,w KQ,Q0 = cGy

where

Percentage Variation with respect to TPS value:

f) RESULTS

i) The measured absolute dose for the given patient at isocentre is ________

ii) The percentage variation with respect to TPS value is _________



22. Verification of Intensity Modulated Radiotherapy plan using 2D

dosimetry

a) AIM

To verify the Intensity Modulated Radiotherapy plan using planar dosimetry.

b) REQUIREMENTS

Verification film/2D array detector, slab phantom, Software to analyze the dose plane (fluence),

TPS, etc,.

c) THEORY

Intensity modulated radiotherapy (IMRT) planning demands stringent quality assurance and

accurate dose determination for delivery of highly conformal dose to the patients. Generally 3-D

dose distributions obtained from a treatment planning system have to be verified by dosimetric

methods. The verification includes absolute dosimetry for all treatment fields and relative

dosimetry for each treatment portal.

The 2D verification of planar dosimetry can be performed using any one of the following system

radiographic film, radiochromic film, 2D array detector or EPID portal dosimetry. The measured

dose distribution has to be compared with the TPS calculated dose. The quantitative comparison

of dose distributions has become a key issue in two dimensional dosimetry with the

implementation of IMRT. Simple evaluation by superimposing isodose distributions can only

highlight or indicate areas of disagreement but does not allow specifying the level of

agreement/disagreement in a quantitative way. The most often applied dose evaluation tools

comprise a direct comparison of dose differences (DD), a comparison of distance-to-agreement

(DTA) between measured and calculated dose distributions, and a combination of these two

parameters is called gamma evaluation method.

The criterion for gamma evaluation is γ ≤ 1 for 3% delta dose and 3 mm DTA.

d) PROCEDURE

This procedure describes about ImatriXX measurement

Use 2mm axial cut CT scan images of I‟mariXX device with 5 cm solid water phantom

positioned above and below.

Using phantom image set, create the verification plan from the patient‟s plan.

Calculate the dose distribution at the detector plane with treatment field.

Transfer the planned information to the analyzing software.

Export all the verification fields to accelerator console.

Set gantry and collimator angles to 0 degree in the verification plan for every single field.

Make the central beam perpendicular to the ImatriXX measurement level at the center of the

measurement area.

Carry out the measurement with I‟mariXX device and compare the measured dose distribution

with TPS calculated dose distribution using Gamma Index method.



Figure: experimental setup for planar dosimetry

The films can also be used in place of ImatriXX device, by following the same procedure.

e) OBSERVATIONS

Patient Name: Hospital No.: RT Number:

Gamma index criteria DD: DTA:

Gantry Angle % of Gamma

pixel match

f) RESULTS

The result shows that the gamma pixel match is ____%. Hence the plan can be accepted for

treatment.



23. Quality Assurance procedure for Dynamic Multi-leaf Collimator

a) AIM

To perform the quality assurance for dynamic multi-leaf collimator.

b) REQUIREMENTS

Slab phantom, ImatriXX/film, TPS, analyzing software, etc,.

c) THEORY

The clinical use of IMRT requires special quality assurance (QA) procedures for machine and

patient specific treatment plan. The machine related QA tests are leaf position accuracy, leaf

position reproducibility, Picket fence test and garden fence test. The standard test patterns like X

wedges, Y wedges, Pyramids and complex fields has to be checked periodically to access the

MLC position. To check the position accuracy of MLC, the gantry and collimator spoke shot has

to be performed with the radiographic film. The leaf transmission and leaf gap width test has to be

performed during the commissioning, to incorporate these information into the treatment planning

system.

For IMRT delivery it is essential to verify the treatment plan before delivery. The verification

includes absolute dosimetry for all treatment fields and relative dosimetry for each treatment

portal. In order to verify the relative dosimetry for each treatment portal, the dose distribution

pattern for chair test and pyramid test can be generated in the treatment planning system.

d) PROCEDURE

1) Static MLC checks: There are tests to verify the leaf position accuracy and leaf position

repeatability for static MLC positions. These tests can be performed using calibrated front

pointer and taping a piece of graph paper to the couch top. 1) Perform the leaf position

accuracy with field opening of leaf positions of 5 cm, -10 cm (A bank MLC), -10 cm and 15

cm (B bank MLC) field opening with MLC (Varian test pattern). 2) Perform the leaf position

repeatability by marking the actual leaf position on the graph paper and executing various

standard test patterns provided by Varian in auto cycle model.

2) DMLC checks: Carryout the Picket fence test and the garden fence test to check the stability

of the dMLC and reproducibility of the gap between leaves. These test patterns can be

performed using I‟matriXX device or film. The picket fence test consists of eight consecutive

leaf movements of a 5-cm wide rectangular field spaced at 5-cm intervals; the field information

is contained in three separate test files which are run in sequence at the accelerator treatment

console. The test field can be exposed using I‟mariXX at 94.6 cm SSD placed over treatment

couch with 5 cm solid water build up (detector plane at 100 cm).

The garden fence test consists of a narrow band (2 mm wide) spaced at 2-cm intervals. Each

leaf match line can be analyzed either visually or by measuring the full-width half-maximum

distance.

3) Analysis of standard tests: The quality assurance test patterns provided by Varian like X

wedges, Y wedges, Pyramids, complex field can be tested using I‟mariXX device/ film. These



tests are designed to achieve a qualitative analysis of the position accuracy of the leaf, kinetic

properties of the dMLC, and a dosimetric evaluation of fractional dose delivery.

4) Treatment delivery verification or TPS plan verification: In treatment planning system, the

dose distribution generated for chair test and pyramid test can be exported to verification

phantoms for quantitative evaluation with I‟mariXX/film dosimetry systems. Compare the

measured and TPS calculated dose distribution patterns for both the tests.

e) OBSERVATIONS

1) Leaf position accuracy for static MLC ____mm

2) Leaf position reproducibility for static MLC is______

3) The stability and reproducibility of dMLC were checked with garden fence test and Picket

fence test. The leaf position errors were checked by visual inspection and profile analysis.

There is no error in the profile analysis.

4) The standard patterns like X wedges, Y wedges and pyramidal tests measured with

I‟mariXX/film were compared with the baseline standard patterns using gamma evaluation

tools. The results are shown below

Gamma evaluation criteria: 3% delta dose, 3mm DTA

Test pattern Percentage of gamma pixel

match

X wedges

Y wedges

pyramidal test

5) Measure the chair and pyramid test dose distribution pattern with I‟matriXX/film. The

measured and TPS calculated dose distribution patterns were compared using gamma

evaluation tools. The results are shown below.

Gamma evaluation criteria: 3% delta dose, 3mm DTA

Test pattern Percentage of gamma pixel

match

Chair test

Pyramid test

f) RESULTS

The dynamic multi-leaf collimator quality assurances were performed. The measured results were

within the limit.



24. Determination of dynamic leaf spacing for dynamic MLC fields

a) AIM

To calculate the dynamic leaf spacing for dynamic multi-leaf collimator .

b) REQUIREMENTS

Pin point chamber, air measurement buildup cap, different sliding window patterns etc,.

c) THEORY

Intensity Modulation Radiotherapy (IMRT) can be delivered by two main modalities namely

segmental IMRT (step and shoot) and dynamic IMRT (sliding window). In the step-and-shoot

modality, the MLC shape remains constant while the beam is on and changes while the beam is

off and in the sliding window, each leaf pair moves continuously, unidirectionally, and with

independent speed while the beam is ON. During dynamic IMRT treatment the gap between the

bounded end the leafs will introduce some leakage radiation in the treatment planning. It is

important to know the leaf gap width for dynamic IMRT delivery and incorporate the same into

treatment planning system.

d) PROCEDURE

Find out the meter reading (M) using a pinpoint chamber with buildup cap in air at isocentre.

Program 10 cm field with varying sliding windows viz., 0.5mm, 1.0mm, 4mm, 10mm and

20mm. For set MU integrate the total readings in the dosimeter. Separately measure the leakage

radiation (Mtr) for set MU and subtract it from the obtained readings. Different sliding windows

have different indexer values, based on the indexer values using the following formula, calculate

the monitor unit to set on the linear accelerator console.

MU = (Dose rate X Field size) / (Index number {third segment} X Velocity X 60)

MU = (400 cGy/min X 10cmx10cm) / (0.9901 X 1 cm/sec x 60)

MU= 50.499

The index values vary for different sliding windows. It is 0.99775 for 0.1 mm, 0.9901 for 1mm,

0.9615 for 4mm, 0.9091 for 10 mm, 0.8333 for 20 mm.

e) OBSERVATIONS

Electrometer: Dose rate: Field size: MLC type:

SCD: 100 cm, In-air measurement with buildup cap.

Calibration factor ND,W= KQ,Q0 (6MV)= KQ,Q0 (18MV)=



Gap width= 0.1mm, Set MU=42

Sl.No. Meter reading

6 MV 18 MV

1

2

3

Avg.

Calculated dose Mg

(cGy)

Gap width= 1mm, Set MU=42


6 MV 18 MV

1

2

3

Avg.

Calculated dose Mg

(cGy)



6 MV 18 MV

1

2

3

Avg.

Calculated dose

Mg(cGy)



6 MV 18 MV

1

2

3

Avg.

Calculated dose Mg

(cGy)





6 MV 18 MV

1

2

3

Avg.

Calculated dose Mg

(cGy)

Open field irradiation Field Size: 10cm x 10cm


6 MV 18 MV

1

2

3

Avg.

Calculated dose

(cGy)

MLC full closed with 10cm x 10cm jaw opening. MU=1000


6 MV 18 MV

1

2

3

Avg.

Calculated dose

(cGy)

Leakage radiation Mtr = (calculated dose for MLC fully closed x set MU for DLS) / 1000

Calculated M for 6MV

Gap (mm) MUcal MUlinac f=(MUcal/ MUlinac) Mg (cGy) Mtr M= (fxMg)- Mtr

0.1

1

4

10

20



Calculated M for 18MV

Gap

(mm)

MUcal MUlinac f=(MUcal/ MUlinac) Mg (cGy) Mtr M= (fxMg)- Mtr

0.1

1

4

10

20

f) RESULTS

i) Plot a graph between Gap and M, find out the DLS from the slope.

ii) The measured DLS for 6 MV is ____mm. DLS for 18 MV is _______mm.



25. Installation planning of Telecobalt therapy

a) AIM

To calculate the wall thickness required to install the telecobalt unit.

b) REQUIREMENTS

Nature of source, workload, use factor, occupancy factor, dimension of the room, machine type,

permissible dose, calculator, etc,.

c) THEORY

The planning of radiotherapy installation is done on the basis of the nature of radioactive source,

workload in terms of cGy/Wk, type of exposure, nature of occupancy all around the room and

dimension of the room. The main aim of planning is to provide adequate wall thickness to

control the radiation level outside the room, which should not be more than 2 mR/wk (0.02

mGy/wk) for general public and 40 mR/wk (0.4 mGy/wk) for radiation worker.

The thickness of wall required to reduce the radiation level outside the room to permissible value

for general public and radiation worker is calculated using the following formula

Reduction Factor (R.F) = WUT / pd2

where W- workload of the machine (cGy/Wk)

U – use factor

T- Occupancy factor

d- distance from source to outside room

p- weekly permissible dose for persons p=0.4 mGy/wk for radiation workers

p=0.02 mGy/wk for general public

d) PROCEDURE



Figure: Typical layout for telecobalt

The typical layout for telecoblat is shown in figure. The minimum inside room dimension should

be 5m x 6m. The walls should be constructed with concrete density of 2.35 g/cm3. The figure

should clearly indicate, the beam central axis, isocentre, axis rotation, conduit, control panel,

door, door with interlock, maze and dimension of walls.

e) CALCULATIONS

The telecobalt workload can be calculated as follow

Workload (W) = 400 cGy/Patient X 80 patients/day X 5 days/wk

= 1.6 x 105 cGy/wk

The use factor U is the fraction of the beam-on time during which the primary beam is directed

towards a particular barrier. The following primary beam use factors are usually assumed for

external beam machines: U (floor) = 1; U (walls) = 0.25; U (ceiling) = 0.25. For all secondary

barriers U is always equal to 1, since secondary radiation is always present when the beam is ON

The occupancy factor T is a factor with which the workload is multiplied to account for the

degree of occupancy of the area in question. Typical values are T (offices) = 1; T (corridors) =

0.25; T (waiting rooms) = 0.125.



1) Calculation for Primary barrier

Consider the left side primary wall (fig) for calculation:

W= 1.6 x 105 cGy/wk

U= 0.25

T= 1

d= 0.8 + 2.5+1.3 = 4.1 m, where 0.8m is isocentre distance, 2.5m is distance from isocentre to

wall, 1.3m is inside the wall to point of interest.

p=0.002 cGy/wk

R. F = WUT / pd2

= 1189.767

log(R.F) = log(1189.767) = 6.075 TVT (1 TVT for concrete for Co-60 is 20.3cm)

Concrete thickness = 6.075 x 20.3 = 123.3 cm

Add 1 HVL for additional safety. Therefore concrete thickness = 123.3+6.15= 129.45 cm

2) Calculation for secondary barrier

Consider the wall towards the console side (fig)

W= 1.6 x 105 cGy/wk

U= 1

T= 1

d= 0.8 + 3+0.5 = 4.3m, where 0.8m is isocentre distance, 3m is distance from isocentre to


p=0.04 cGy/wk (At the console)

The scattering coefficient „a’ depends on the photon beam energy and scattering angle. It‟s

typical value for 90º scatter is 10–4

–10–3

.

‘a’ is the ratio of the scattered radiation at 1 m from the scattering object (patient) to the primary

radiation at 1 m.

R. F = 10-3

WUT / pd2

= 216.33

log(R.F) = log(216.33) = 2.335 TVT (1 TVT of concrete for Co-60 is 20.3 cm)

Concrete thickness = 2.335 x 20.3 = 47.4 cm

Add 1 HVL for additional safety. Therefore concrete thickness = 47.4+6.15= 53.55 cm.

f) RESULTS

The barrier thickness calculation was carried out for telecobalt installation.

1TVT = I0/10 I = I0/10n

2TVT = I0/102

R.F = I0/I = 10n

3TVT = I0/103

log(R.F) = n

nTVT = I0/10n



26. Installation planning of High Energy Linear Accelerator

a) AIM

To calculate the wall thickness required to install the high energy linear accelerator.

b) REQUIREMENTS

Energy, workload, use factor, occupancy factor, dimension of the room, machine type,

permissible dose, calculator, etc,.

c) THEORY

The planning of radiotherapy installation is done on the basis of energy of linear accelerator,

workload in terms of cGy/Wk at 1 m distance from the source, type of exposure, nature of

occupancy all around the room and dimension of the room. The main aim of planning is to

provide, adequate wall thickness to control the radiation level outside the room, which should not

be more than 2 mR/wk (0.02 mGy/wk) for general public and 40 mR/wk (0.4 mGy/wk) for

radiation workers.

The main components of a typical linac installation are the treatment room, entrance maze,

control room and optional mechanical–electrical room. The maze connects the treatment room

with the control room, which houses the operational controls of the linac. The treatment room

and maze together are called the linac bunker.

The thickness of wall required to reduce the radiation level outside the room to permissible value

for general public and radiation worker is calculated using the following formula


where W- workload of the machine (cGy/Wk)

U – use factor

T- Occupancy factor



p=0.02 mGy/wk for general public.

ICRP Publication 33 (para. 256) stating that actual dose values to individuals in the occupied

areas are to be 1/10 (for equivalent dose) to 1/30 of the effective dose used as the shielding

design parameter. This is due to a number of conservative assumptions made in the calculation.

The general public dose acceptable limit further drops to (Hlimit) 0.3 mSv/year for shielding

calculation.

d) PROCEDURE

The typical layout for 15MV dual energy linear accelerator is shown in figure. The minimum

inside room dimension should be 6m x 7m. The walls should be construction with concrete

density of 2.35 g/cm3. The figure should clearly indicates, the beam central axis, isocentre, axis

rotation, conduit, control panel, door, door with interlock, maze and dimension of walls.



Figure 1: Typical layout for Linear Accelerator

e) CALCULATION

A 15 MV linear accelerator consists of dual photon beams and electron beams. Photon energies

6 MV and 15 MV and multiple electron energies. The workload should be considered for both

higher and lower energy. However, for shielding calculation the higher energy workload should

be taken into consideration.

Clinical workload Wclin (6 MV) = 330 cGy/Patient X 50 patients/day X 5 days/wk x 52 wks

= 42.9 x 105 cGy/year

Physics and electronic workload Wcal includes routine calibration, QA and phantom

measurement. A conservative estimate is 7.1 x105 cGy/year.



Total accelerator workload per year = 42.9 x 105 +7.1 x10

5 = 50 x 10

5 cGy/year

= 1.0 x 105 cGy/wk

Clinical workload Wclin (15 MV) = 330 cGy/Patient X 25 patients/day X 5 days/wk x 52 wks

= 21.45 x 105 cGy/year

Physics and electronic workload Wcal includes routine calibration, QA and phantom

measurement. A conservative estimate is 7.1 x105 cGy/year.

Total accelerator workload per year = 21.45 x 105 +7.1 x10

5 = 28.55 x 10

5 cGy/year

= 5.5 x 104 cGy/wk

The use factor U is the fraction of the beam-on time during which the primary beam is directed

towards a particular barrier. The following primary beam use factors are usually assumed for

external beam machines: U (floor) = 1; U (walls) = 0.25; U (ceiling) = 0.25. For all secondary

barriers U is always equal to 1, since secondary radiation is always present when the beam is

ON.

The occupancy factor T is a factor with which the workload is multiplied to account for the

degree of occupancy of the area in question. Typical values are T (offices) = 1; T (corridors) =

0.25; T (waiting rooms) = 0.125.

1) Calculation for primary barrier

Thickness required for 15 MV


W= 5.5 x 104 cGy/wk

U= 0.25

T= 0.25

d= 1 + 3+2.2 = 6.2m, where 1.0m is isocentre distance, 3m is distance from isocentre to


p=Hlimit = 5.76x10-4

cGy/wk

R. F = WUT / pd2

= 155542.98

log(R.F) = log(155542.98) = 5.192 TVT (1 TVT of concrete for 15 MV is 46 cm)

Concrete thickness = 5.192 x 46 = 239 cm

Thickness required for 6 MV


W= 1.0 x 105 cGy/wk

U= 0.25

T= 0.25




cGy/wk

R. F = WUT / pd2

= 282805.429




Concrete thickness = 5.45 x 35= 190.8 cm.

Hence, 15MV shielding will be adequate for 6MV photons.

If 239 cm wall is provided, the dose outside the room for 6MV beam will be

D= WUT/(RF)d2 = (1.0 x 10

5 x 0.25 x 0.25)/((6.2)

2 x 10

239/35)

= 2.258 x 10-5

cGy/wk

Width of primary field With reference to the figure, in the primary wall, the primary field region require more thickness

and remaining part of the wall is required for considering the leakage radiation.

The maximum field size at isocentre is 40cm x 40cm with a diagonal length of 56.6 cm. The

width w of the primary barrier placed symmetrically about the linac beam central axis is

calculated as

w = 0.566 (d/d0) + 0.6 meter

where d0 – source to axis distance, d- distance from target to the distal end of the primary wall

and 0.6m (2 ft) added to provide safety margin.

w = 0.566 (4/1) + 0.6 = 286.4 cm

Backside of the primary wall (Leakage barrier)

The calculation of head leakage barrier transmission factor is carried out assuming an attenuation

due to accelerator shielding L0 = 0.001.

W= 5.5 x 104 cGy/wk

U= 1

T= 0.25




cGy/wk

R. F = 10-3

WUT / pd2

= 622.17


Concrete thickness = 2.794 x 46 = 129 cm

2) Calculation for secondary barrier (scatter barrier)

W= 5.5 x 104 cGy/wk

U= 1

T= 0.25

d= 1 + 3.5+1.4 = 5.9m, where 1.0m is isocentre distance, 3.5m is distance from isocentre to

wall, 1.4m is inside of the wall to point of interest.


cGy/wk



The scattering coefficient „a’ depends on the photon beam energy and scattering angle. It‟s

typical value for 90º scatter is 10–4

–10–3

.

‘a’ is the ratio of the scattered radiation at 1 m from the scattering object (patient) to the primary

radiation at 1 m.

R. F = 10-3

WUT / pd2

= 685.785


Concrete thickness = 2.836 x 46 = 130.0 cm

If 130 cm wall is provided, the dose outside the room for 6MV beam will be

D= WUT/(RF)d2 = (1x10

-3x1.0 x 10

5 x 0.25 x 1.0)/((5.9)

2 x 10

130/35)

= 1.386 x 10-4

cGy/wk.

3) Ceiling

W= 5.5 x 104 cGy/wk

U= 0.25

T= 1

d= 3-1.3+1+2.2 = 4.9m, where 1.0m is isocentre distance, 3m is inside room dimension,

1.3m is the isocentre distance from the ground, 2.2 m is inside the wall to point of

interest.


cGy/wk

R. F = WUT / pd2

= 996376.8


Concrete thickness = 5.998 x 46 = 276 cm.

Width of primary field w = 0.566 (2.7/1) + 0.6 = 212.8 cm

Backside of the primary wall (Leakage barrier)

The calculation of head leakage barrier transmission factor carried out assuming an attenuation

due to accelerator shielding of L0 = 0.001.

W= 5.5 x 104 cGy/wk

U= 1

T= 0.25

d= 3-1.3+1+2.2 = 4.9m, where 1.0m is isocentre distance, 3m is inside room dimension,

1.3m is the isocentre distance from the ground, 2.2 m is inside the wall to point of

interest.


cGy/wk

R. F = 10-3

WUT / pd2

= 996.38


Concrete thickness = 2.998x 46 = 138cm.



Oblique incident

Figure 2: Slant thickness from oblique incident radiation beam

Radiation may approach a barrier at an oblique angle. In this case the slant thickness can be

calculated as radiation path length„t‟ of the incident beam is given by

t= s/cosƟ

where Ɵ is the angle of the beam with respect to a line perpendicular to the barrier and s is the

perpendicular thickness of the barrier. Some scatter will not stay on this path as represented by a

in the figure. Hence as a rule of thumb one or two HVLs are added to the calculated barrier

thickness to compensate for this effect.

Ceiling thickness at door position

Figure 3: Represent the diagonal length

d = √42+4

2 = 5.66 m

R.F = (1x10-3

x5.5 x 104 x 1.0 x 1.0)/((5.66)

2 x 5.76x10

-4)

= 27972.97



log(R.F) = log(27972.97) = 3.473 TVT (1 TVT of concrete for 15 MV is 46cm)

Concrete thickness = 3.473 x 46 = 160cm.

Oblique correction factor = 160 x cos 45

= 113.13 cm.

1 HVL of concrete for 15 MV is 13.8 cm.

Then, the required ceiling thickness at the door position is 113.13+13.8 = 127cm.

f) RESULTS

The barrier thickness calculation was carried out for 15MV linear accelerator installation.



27. Installation planning of High Dose Rate Brachytherapy

a) AIM

To calculate the barrier thickness required to install high dose rate (HDR) brachytherapy unit.

b) REQUIREMENTS

Source type, Maximum Activity, workload, use factor, occupancy factor, dimension of the room,

machine type, permissible dose, calculator, etc,.

c) THEORY

HDR brachytherapy treatment rooms are designed with similar constraints as are linac and

teletherapy rooms. There is, however, one major difference: in brachytherapy rooms all walls are

primary barriers, since the source can generally be positioned anywhere in the room and the

radiation is emitted isotropically and uncollimated from the source. The attenuation in the patient

is not considered in primary barrier transmission calculations. The workload specification is

given in terms of air kerma in air per week or year. 192

Ir facility is determined using the following data:

The typical workload specification for a remote afterloading HDR

Maximum source activity: 370 GBq (10 Ci).

Maximum number of patients treated: 10/day.

Number of working days (or treatment days) per week: 5 days/week.

Maximum treatment time: 10 min (for 10 Ci) per patient.

Air kerma rate constant for 192

Ir: 111 mGy·m2/(GBq·h) = 4.1 µGy·m

2/(mCi·h)

Workl oad: W = 104x10x5x10x(1/60)x4.1 µGy·m

2/wk

= 3.4x105 µGy·m

2/wk= 3.4x10

2 mGy·m

2/wk


where

U – use factor (U=1, all walls receive primary radiation)

T- Occupancy factor (T=1 consider full occupancy)



p=0.02 mGy/wk for general public.

d) PROCEDURE

The typical layout for HDR Ir-192 brachytherapy is shown in figure. The minimum inside room

dimension should be 4m x 5m. The walls should be construction with concrete density of 2.35

g/cm3. The figure should clearly indicates, the Ir-192 source position during ON condition,

conduit, control panel, door, door with interlock, maze and dimension of walls.



Figure: Typical layout for HDR Brachytherapy

e) CALCULATION

1) Calculation for wall I

W= 3.4x102 mGy·m

2/wk

U=T= 1

P= 0.02 mGy/wk

d=2+0.45= 2.45 ( 2m distance from source to wall, 0.45m is inside the wall to point of

interest)

R. F = WUT / pd2

= 2832.15

log(R.F) = log(2832.15) = 3.45TVT (1 TVT of concrete for Ir-192 is 13.5cm)

Concrete thickness = 3.45 x 13.5 = 46.6 cm.

2) Calculation for maze wall (II)

W= 3.4x102 mGy·m

2/wk

U=T= 1

P= 0.4 mGy/wk

d=2+0.3= 2.3m ( 2m distance from source to wall, 0.30 m is inside of the maze wall to point

of interest)

R. F = WUT / pd2

= 160.68




Concrete thickness = 2.21 x 13.5 = 30.0cm.

3) Calculation for wall (II) outside

W= 3.4x102 mGy·m

2/wk

U=T= 1

P= 0.4 mGy/wk

d=2+0.3+1.5+.25 = 4.05m ( 2m distance from source to wall, 0.30m maze wall thickness,

1.5m space between maze wall to outside wall, 0.25m is inside of the wall the point of

interest)

R. F = WUT / pd2

= 51.821


Concrete thickness = 1.714 x 13.5 = 23.14 cm.

4) Calculation for wall (III)

W= 3.4x102 mGy·m

2/wk

U=T= 1

P= 0.02 mGy/wk

d=2.5+0.45= 2.95 (2.5m distance from source to wall, 0.45m is inside of the wall to point

of interest)

R. F = WUT / pd2

= 1953.46



5) Calculation for wall (IV) console

W= 3.4x102 mGy·m

2/wk

U=T= 1

P= 0.02 mGy/wk

d=2+0.4= 2.4 (2m distance from source to wall, 0.40m is inside of the wall to point

of interest)

R. F = WUT / pd2

= 2951.38



f) RESULTS

The barrier thickness calculation was carried out for HDR Ir-192 brachytherapy installation.



28. Radiation Protection Survey of Telecoblat Machine

a) AIM i) To determine the stray radiation from telecobalt source head during source ON and OFF

condition.

ii) To perform the radiation protection survey for telecobalt installation

b) REQUIREMENTS

Telecobalt unit, survey meter, shielding blocks, layout plan, measuring tape, etc.,

c) THEORY

Protection is required against three types of radiation: the primary radiation, the scattered

radiation, and the leakage radiation through the source housing. A barrier sufficient to attenuate

the useful beam to the required degree is called the primary barrier. The required barrier against

stray radiation (leakage and scatter) is called the secondary barrier.

i) The leakage radiation from the source housing with the beam in “OFF” position

a) Shall not exceed 0.2 mGy/h (20 mR/h) at 5 cm distance from the surface of source head

b) At 1 m from the source shall not exceed 0.02 mGy/hr (2 mR/h).

ii) The absorbed dose rate due to leakage radiation during „ON‟ condition, measured at a

distance of 1 m from the radiation source shall not exceed 0.5% of the maximum absorbed

dose rate on the radiation beam axis measured at distance of 1 m from the radiation source

(The leakage from source in source „ON‟ position at 1 m from the source with collimator jaws

completely blocked with 3 TVT of lead shall not exceed 0.1% of RMM of loaded source).

iii) Area survey: Radiation exposure level at various locations in and around the teletherapy

room has to be checked in order to ensure the protection of radiation worker and general

public. The weekly permissible dose for radiation worker is 40 mR/wk (0.4 mGy/wk) and 2

mR/wk (0.02 mG/wk) for general public.

d) PROCEDURE i) Measure the source head leakage at various points during both beam „ON‟ and „OFF‟

conditions using GM based survey meter.

ii) T h e r a d i a t i o n l e v e l c a n b e m e a s u r e d u s i n g w a t e r p h a n t o m o f s i z e 3 0 x 3 0 x 3 0 c m

3a t n o m i n a l t r e a t m e n t d i s t a n c e w i t h m a x i m u m f i e l d

s i z e . T h e F i g u r e i n d i c a t e s clearly areas occupied by radiation, non-radiation workers and members of public. The locations are marked as 1, 2, 3, ….etc. Measure the exposure rates (mR/h) at cardinal gantry positions are 0

0, 90

0, 180

0 & 270

0.

iii) Primary barrier adequacy: Direct the primary beam with fully opened apertures towards

primary walls, ceiling and floor – if basement exists – and measure the shielding

adequacy of the primary barriers. Records your observations in the table.



Figure: Typical layout for Telecobalt

e) OBSERVATIONS

Machine: Survey Instrument used: Date of Measurement:

Head Leakage measurement:

Source ‘OFF’ condition

Measured exposure rate (mR/h) at

Measurement positions

1 2 3 4 5 6 7 8

5 cm from the surface of the source head

1 m from the source

Source ‘ON’ condition Measured exposure rate at 1m from the source with collimator jaws completely blocked with

appropriate lead thickness

Maximum :

Minimum :

Tolerance : < 0.1 % of RMM of the loaded source.

Radiation survey:

As shown in the figure, the locations are marked as 1, 2, 3,.etc. Measured exposure rates (mR/h) at cardinal gantry positions 0

0, 90

0, 180

0 & 270

0 are shown below.



Gantry Angle

Measured exposure Rate (mR/h) At positions (1….10)

1 2 3 4

5 6 7 8 9

Primary Barrier adequacy:

Positions 1 2 3 4 5 6 Avg

Primary barrier 1

Primary barrier 2

Above ceiling

Below floor

f) RESULTS

i) The stray radiation measured from the telecobalt source head is within the acceptable limit.

ii) The radiation protection survey has been performed for the telecobalt machine and the

measured radiation levels are within the acceptable limit.



29. Radiation Protection Survey of High Energy Linear Accelerator

a) AIM i) To determine the stray radiation from Linear Accelerator head during beam ON condition.

ii) To perform the radiation protection survey of high energy linear Accelerator.

b) REQUIREMENTS

Linear Accelerator, ionization chamber survey meter, shielding blocks, layout plan, measuring

tape, etc.,

c) THEORY

Protection is required against three types of radiation: the primary radiation, the scattered

radiation, and the leakage radiation through the linear accelerator head. A barrier sufficient to

attenuate the useful beam to the required degree is called the primary barrier. The required

barrier against stray radiation (leakage and scatter) is called the secondary barrier.

Leakage radiation is the radiation that emerges from the linear accelerator treatment head

through its protective barriers. Besides, in an electron accelerator, some of the electrons being

accelerated may hit wave-guide tube and thus produce off-target radiations. Accelerators

operating at potentials 10 MV or above produce unwanted neutrons with a range of energies.

Contributions of each component must be evaluated separately. It is mandatory to keep leakage

radiation levels within the limit prescribed by the national competent authority.

i) Kerma rate due to leakage radiations (excluding neutrons) at any point outside the useful beam

but inside a plane circular area of radius 2 m centered around and perpendicular to the central

axis of the beam at normal treatment distance is 0.2% of the air kerma rate on the axis at same

distance.

ii) Kerma rate due to leakage radiations (excluding neutrons) at 1 m from the path of electrons

between their origin and the target or electron window is 0.5% of the air kerma rate on the

central axis of the beam.

iii) Area survey: Radiation exposure level at various locations in and around the teletherapy

room has to be checked in order to ensure the protection of radiation worker and general

public. The weekly permissible dose for radiation worker is 40 mR/wk (0.4 mGy/wk) and 2

mR/wk (0.02 mG/wk) for general public.

d) PROCEDURE i) Measure the leakage radiation at various points during „ON‟ conditions using Ionization

chamber based survey meter.

ii) The leakage radiation through the source housing in beam "ON" position should be measured

as follows: Choose 16 measurement points located on the surface of a sphere of radius 1 m

from the source. Take 2 points on the poles of the sphere, 4 equally spaced points on its

equator and distribute the remaining points uniformly on the surface of the sphere. Close the

diaphragms completely with at least 3 TVL of lead or any other suitable shielding material.

Measure air kerma rates at these 16 points individually. Ensure that the kerma rates due to

leakage radiation are within the prescribed limits given above.

iii) T h e r a d i a t i o n l e v e l c a n b e m e a s u r e d u s i n g w a t e r p h a n t o m o f



s i z e 3 0 x 3 0 x 3 0 c m3

a t n o m i n a l t r e a t m e n t d i s t a n c e w i t h m a x i m u m f i e l d s i z e . S e l e c t t h e h i g h e s t d o s e r a t e a n d e n e r g y f o r s u r v e y m e a s u r e m e n t . T h e F i g u r e i n d i c a t e s clearly areas occupied by radiation, non-radiation workers and members of public. The locations are marked as 1, 2, 3, ….etc. Measure the air kerma rates (mSv/h) at cardinal gantry positions 0

0, 90

0, 180

0 &

2700.

Figure: Typical layout for linear accelerator

e) OBSERVATIONS

Machine: Energy: Dose rate: Survey Instrument used: Date of Measurement:

Head Leakage measurement:

Source ‘ON’ condition

i) Kerma rate due to leakage radiations (excluding neutrons) at any point outside the useful beam

but inside a plane circular area of radius 2 m centred around and perpendicular to the central

axis of the beam at normal treatment distance Maximum:

Minimum: ii) Kerma rate due to leakage radiations (excluding neutrons) at 1 m from the path of electrons

between their origin and the target or electron window Maximum:

Minimum:



Radiation survey:

As shown in the figure, the locations are marked as 1, 2, 3, ….etc. Measured Kerma rates (mSv/h) at cardinal gantry positions 0

0, 90

0, 180

0 & 270

0are shown below.

Gantry Angle

Measured Kerma Rate (mSv/h) At positions (1….10)

1 2 3 4

5 6 7 8 9

f) RESULTS

i) The stray radiation measured from the linear accelerator treatment head is within the

acceptable limit.

ii) The radiation protection survey has been performed for the high energy linear accelerator and

the measured radiation levels are within the acceptable limit.



30. Radiation Protection Survey of Low Dose Rate Manual

afterloading Brachytherapy facility

a) AIM

i) To perform autoradiograph and swipe test to check the integrity of manual afterloading

brachytherapy source. ii) To measure stray radiation from brachytherapy storage container and in-house transport

container.

iii) To perform the radiation protection survey of LDR manual brachytherapy facility.

b) REQUIREMENTS

Brachytherapy source, Survey meter, Contamination monitor, Radiographic/Gafchromic film,

layout plan, measuring tape, etc,.

c) THEORY

Brachytherapy is a method of treatment with sealed radioactive sources. They are used to deliver

radiation at a short distance by interstitial, intracavitary, or surface application. With this mode

of therapy, a high radiation dose can be delivered locally to the tumor with rapid dose fall-off in

the surrounding normal tissue. In the past, brachytherapy was initiated with radium or radon

sources. Currently, the artificially produced radionuclides such as 137

Cs, 192

Ir, 198

Au, 125

I, and 103

Pd are being used.

Manual afterloading brachytherapy: The radiation sources are manually afterloaded into

applicators or catheters that have been placed within the target volume. At the end of the

treatment the sources are removed, again manually. These procedures result in some radiation

exposure to the medical and support staff. Low Dose rate (about 0.4–2 Gy/h) brachytherapy

sources are being used in the manual afterloading brachtherapy.

Manual afterloading brachytherapy facility: The manual afterloading brachytherapy facility

should include brachytherapy Operation Theatre (OT), Permanent and temporary storage

container, L-Bench, Mobile shielding, Handling tools, In-house transport container, Lead pots,

Shielding blocks, etc,.

Integrity of brachytherapy sources: The source integrity has to be checked quarterly by

performing autoradiograph and swipe test.

Stray radiation from brachytherapy storage containers: Brachytherapy source storage, in-

house transport containers shall meet the following limits for leakage radiation level.

Brachytherapy source

storage and in-house

transport containers

Leakage Radiation dose rate (µGy/hr)

5 cm from surface of storage 1 m from

source

Portable 500 20

Mobile 1000 50

Area survey: Radiation exposure levels has to be measured at various locations in the LDR

manual afterloading brachytherapy facility in order to ensure the protection of radiation worker



and general public. The weekly permissible dose for radiation worker is 40 mR/wk (0.4

mGy/wk) and 2 mR/wk (0.02 mG/wk) for general public.

d) PROCEDURE

i) Integrity of brachytherapy sources: The swipe test of the brachytherapy source has to be

performed using wet cotton and long forceps. Measure the background counts and actual

counts using contamination monitor. Use Radiographic/Gafchromic film to obtain the

autoradiogrph.

ii) Stray radiation from brachytherapy storage containers: This test has to be performed with

calibrated GM monitor.

iii) Radiation survey: Figure indicates the area of manual after loading brachytherapy ward and

hot lab. The measurement locations are marked as A, B, C,. etc,.

Figure: Layout for Manual Brachytherapy facility

e) OBSERVATIONS

Source:

Total Activity:

Survey Instrument used: Contamination monitor used:

Date of Measurement:



i) Integrity of brachytherapy source

Source

type

Activity (mCi) Swipe test result

(c/sec)

Remarks on

Autoradiograph

Remarks about

source integrity

ii) Stray Radiation from brachytherapy Storage Containers (Express in µSv/h or mR/h)

Type of container used

for storage

(Permanent/Temporary)

Source used

for storage

Activity stored at

the time of

measurement (mCi)

Maximum radiation level

5 cm from

surface

100 cm from

source

iii) Radiation survey: Figure above indicates the area of manual after loading brachytherapy

ward and hot lab. The measured radiation levels with respect to the locations marked (A, B,

C,. etc,.) are shown below.

f) RESULTS

i) The source integrity was checked and it can be used for clinical purpose.

ii) The stray Radiation from the brachytherapy storage containers is within the acceptable limit.

iii) The measured radiation levels in and around the manual brachytheapy facility are within the

acceptable limit.

Positions Measured exposure rate (mR/hr)

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O



31. Radiation Protection Survey of High Dose Rate Remote

afterloading Brachytherapy facility

a) AIM

i) To measure the stray radiation from HDR remote afterloading brachytherapy unit.

ii) To perform the radiation protection survey of HDR remote afterloading brachytherapy

facility.

b) REQUIREMENTS

HDR brachytherapy unit, survey meter, layout plan, measuring tape, etc,.

c) THEORY

Brachytherapy is a method of treatment in which sealed radioactive sources are used to deliver

radiation at a short distance by interstitial, intracavitary, or surface application. With this mode

of therapy, a high radiation dose can be delivered locally to the tumor with rapid dose fall-off in

the surrounding normal tissue. The artificially produced radionuclides such as 137

Cs, 192

Ir, 198

Au, 125

I, and 103

Pd are being used for brachytherapy treatment.

HDR Remote afterloading brachytherapy: Remotely controlled afterloading devices are now

available that eliminate the direct handling of the radioactive sources. In addition, the sources

can be instantly loaded and unloaded, making it possible to provide patient care with the sources

retracted into their shielded position. Remote afterloaders are available for either low-dose rate

(LDR) or high-dose rate (HDR) brachytherapy and for interstitial or intracavitary treatments. The

HDR remote afterloader treatments are performed in a fully shielded room with safety

requirements comparable with those required for a cobalt teletherapy unit. For example, the

walls are shielded, the room is equipped with door interlocks that retract the source when the

door is opened or when the emergency button is pushed, radiation monitors are installed with

visible and audible alarms, the patient is monitored via remote closed-circuit television camera

and intercommunication devices, and the emergency procedures are posted at the control station.

HDR source: HDR remote afterloading treatments are achieved by moving a single high-

strength (e.g., 10 Ci) 192

Ir source, welded to the end of a flexible cable, through one or many

available channels. The source can be precisely positioned at any point in the implanted catheters

or applicators. By programming dwell position and dwell time of the source, desired isodose

distributions can be obtained. These high-dose rate units can be used for interstitial,

interaluminal or intracavitary implants.

Stray radiation from brachytherapy unit: Brachytherapy source storage, emergency storage

containers shall meet the following limits for leakage radiation level.

Remote afterloading

Brachytherapy unit

Leakage Radiation dose rate (µGy/hr)

5 cm from surface of storage 1 m from

source

Unrestricted access 10 1

Restricted access 100 10



Area survey: A Radiation exposure level has to be measured at various locations of in and

around HDR Brachytherapy unit installation, in order to ensure the protection of radiation

worker and general public. The weekly permissible dose for radiation worker is 40 mR/wk (0.4

mGy/wk) and 2 mR/wk (0.02 mG/wk) for general public.

d) PROCEDURE

i) Stray radiation from brachytherapy storage containers: This test has to be performed with

calibrated GM monitor.

ii) Radiation survey: In the Figure below, mark the occupancy on all sides, above and below the

installation and measure the maximum dose rates at these locations, with the applicator loaded

with maximum source activity and kept at the centre of the treatment table.

Figure: Typical layout for HDR Brachytherapy facility

e) OBSERVATIONS

Source:

Activity:

Survey Instrument used:

Date of Measurement:



i) Stray radiation from brachytherapy unit (Express in µSv/h or mR/h)

Source used

for storage

Activity stored at

the time of

measurement (Ci)

Maximum radiation level

5 cm from

surface

100 cm from

source

ii) Radiation survey: Figure above indicates the area of HDR brachytherapy unit installation.

The measured radiation levels with respect to the locations marked (A, B, C,. etc,.) are shown

below.

f) RESULTS

i) The stray radiation from HDR brachytherapy unit is within the acceptable limit.

ii) The measured radiation levels in and around the HDR brachytheapy facility is within the

acceptable limit.

Positions Measured exposure rate (mR/hr)

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O



32. Installation planning of Diagnostic X-ray unit

a) AIM

To plan the diagnostic X-ray unit installation.

b) REQUIREMENTS

Type of X-ray machine, Maximum mA, workload, use factor, occupancy factor, dimension of

the room, calculator, etc,.

c) THEORY

Rooms housing diagnostic X-ray units and related equipment shall be located as far away as

feasible from areas of high occupancy and general traffic, such as maternity and pediatric wards

and other departments of the hospital that are not directly related to radiation and its use. The

Shielding provided for the X-ray room barriers must be adequate to reduce radiation levels to

personnel, patients, and the general public to meet the guidelines established by NCRP. "Basic

Radiation Protection Criteria" required is a function of the following:

(a) Type of material in the barrier,

(b) Orientation of the x-ray beam in the room,

(c) Workload of the x-ray unit,

(d) Size of the room and the equipment layout, and

(e) Degree of occupancy in the adjoining areas.

One cannot arbitrarily assume that a given thickness of Lead will be appropriate on all barriers.

Existing records of room barrier design and the report of the shielding evaluation should be

reviewed.

Leakage radiation from X-ray tube housing: Leakage radiation level from X-ray tube housing

at 1m from the target should not exceed 100mR in 1 hr. The maximum workload of an X-ray

unit in one hour is 180 mA.min.

d) PROCEDURE

Figure: Typical layout for Diagnostic X-ray installation



The room housing an X-ray unit shall be not less than 18 m2

for general purpose radiography

and conventional fluoroscopy equipment. The wall thickness should not be less than 23 cm brick

or 15 cm concrete. The layout of rooms in an X-ray installation shall be such that the number of

doors for entry to the X-ray rooms shall be kept to the minimum. The unit shall be so located

that it shall not be possible to direct the primary X-ray beam towards dark room, door, windows,

and control panel, or areas of high occupancy. Appropriate structural shielding shall be provided

for walls, doors, ceiling and floor of the room housing the X-ray unit so that doses received by

workers and the members of public are kept to the minimum and shall not exceed the respective

annual effective doses as prescribed by the competent authority.

e) CALCULATION

Calculation of workload: Weekly radiation level will depend upon the workload of the

particular installation. Workload is measured in terms of mA.min/week as the total output of the

X-ray machine per week depends upon the total mA.min used per week.

S.No. Type of

examination

No. of

patients/wk (1)

No. of

exposures /

patient (2)

Avg.

mAs/exposure

(3)

mAs/wk=

(1)x(2)x(3)

1 Chest 30 1 15 450

2 Head 12 2 80 1920

3 Abdomen 5 1 100 500

4 I.V.P 3 5 100 1500

5 Extremities 35 2 10 700

Total mAs/wk due to all the examinations 5070

Workload = No. patients/wk X No. exposures/patient X Avg. mAs/exposure

= 5070/60 mAmin/wk

= 84.5 mAmin/wk

User factor (U) =1,

Occupancy Factor (T) is the fraction of time a particular place is occupied by staff, patients or

public has to be conservative, ranges from 1 for all work areas to 1/20 for toilets and 1/40 for

unattended car park.

Calculation of weekly exposure level

If 200 mR/hr is the exposure level measured at a point with 50 mA current and 84.5 mA.min/wk

is the workload of the unit then the total weekly exposure level at that point can be calculated as

follows:

Exposure level at that point = (200/50) mR/mA.hr

= 0.0667 mR/mA.min

Total weekly exposure (mR) = 0.0667 mR/mA.min x 84.5 mAmin/wk

= 5.636 mR/wk.

f) RESULTS

The installation planning of diagnostic X-ray unit was performed.



33. Installation planning of Diagnostic CT scanner

a) AIM

To plan the diagnostic CT scanner unit installation.

b) REQUIREMENTS

Type of CT scanner unit, Maximum mA, workload, use factor, occupancy factor, dimension of

the room, calculator, etc,.

c) THEORY

Since CT machines use a narrow beam collimated to an array of shielded detectors, exposure to

the primary beam is only possible for the patient. Any required shielding would be for scattered

radiation. Rooms housing diagnostic CT scanner shall be located as far away as feasible from

areas of high occupancy and general traffic, such as maternity and pediatric wards and other

departments of the hospital that are not directly related to radiation and its use. The Shielding

provided for the CT room barriers must be adequate to reduce radiation levels to personnel,

patients, and the general public to meet the guidelines established by NCRP. "Basic Radiation

Protection Criteria" required is a function of the following:

(a) Type of material in the barrier,

(b) Workload of the CT scanner,

(c) Size of the room and the equipment layout, and

(e) Degree of occupancy in the adjoining areas.

One cannot arbitrarily assume that a given thickness of Lead will be appropriate on all barriers.

Existing records of room barrier design and the report of the shielding evaluation should be

reviewed.

d) PROCEDURE

The room housing an X-ray CT should have minimum dimension of 4m x 8.25 m including

console.



Figure: Typical layout for Diagnostic CT scanner

e) CALCULATION

CT workloads are best calculated from local knowledge. Remember that new spiral CT units, or

multi-slice CT, could have higher workloads, A typical CT workload is about W= 28,000 mA-

min per week.

A CT scanner is placed in a room as shown in figure. The height of the ceiling is 4.0m. The walls

are made of concrete, with a minimum thickness of 15cm. The scanner isocentre is located 0.9m

above floor level.

f) RESULTS

The installation planning of diagnostic CT unit was performed.



34. Radiation protection survey of diagnostic X-ray Installation

a) AIM

To perform the radiation protection survey for Diagnostic X-ray installation.

b) REQUIREMENTS

Diagnostic X-ray unit, Ionization chamber survey meter, measuring tape, water phantom etc,.

c) THEORY

It is necessary to carry out radiological protection survey of the X-ray installation to determine

whether it is safe from radiation protection point of view. During the protection survey radiation

levels in and around the installation, at the places occupied by persons are measured. To simulate

the scattering of X-rays by the patient, a suitable phantom filled with water is used. Ionization

chamber type survey meter is ideal for survey. Maximum kVp should be used during survey. The

higher values of tube current should not be used, the higher mAs may damage the tube. All the

exposure parameters i.e., operating potential (kVp), operating current (mA) and exposure time

(sec) must be recorded and kept constant during survey.

Calculation of workload: Weekly radiation level will depend upon the workload of the

particular installation. Workload is measured in terms of mA.min/week as the total output of the

X-ray machine per week depends upon the total mA.min used per week.

Workload = No. patients/wk X No. exposures/patient X Avg. mAs/exposure

= mAs/wk

Leakage radiation from X-ray tube housing: Leakage radiation level from X-ray tube housing

at 1m from the target should not exceed 100 mR in 1 hr. The maximum workload of an X-ray

unit in one hour is 180 mA.min.

d) PROCEDURE

i) Measure the tube leakage at 1 m from the target using ionization chamber survey meter.

ii) Place the water phantom or plastic bucket filled with water at 1 m distance from the target. Set

maximum kVp and minimum time and required mA. Conduct the radiation survey at various

locations with reference to the figure using ionization chamber survey meter.

e) OBSERVATIONS

X-ray Machine Make: Model: Sl.No.:

Workload: 100 mA.min/week (Approx.)



Figure: Typical layout for Diagnostic X-ray installation

Maximum kVp: mAs: mA.min:

Leakage radiation from X-ray tube: _____ mR/hr

Calculate: ______mR/mA.min,

Calculate (mR/wk) = workload X mR/mA.min

Measured radiation level at various locations

Locations Measured mR/hr

(1)

Calculated mR/mA.min

(2) = (1) X mA.min

Calculated mR/wk

(3)= (2) X workload

Door

Behind chest stand

Wall 1

Wall 2

f) RESULTS

i) The leakage radiation from the X-ray tube housing is within the acceptable limit.

ii) The measured radiation levels in and around the X-ray installation is within the acceptable

limit.



35. Installation planning of Nuclear Medicine High dose Therapy

a) AIM

To plan the high dose therapy nuclear medicine facility.

b) REQUIREMENTS

Number of diagnostic equipments to be installed, No. of beds required for I-131 therapy,

Administration room facility, Types of sources, etc.

c) THEORY

The distribution of radioactivity in the patient body is imaged in the nuclear medicine diagnosis.

The Nuclear Medicine (NM) department should be located away from the main hospital busy

area. Ideally in the corner of the hospital, there should be a good access for patients. The facility

should include separate patients and staff area, imaging rooms, patient‟s reception and waiting

area, cardiac stressing room, administration room, hot lab and separate I-131 therapy ward for

male and female. While designing the NM facility time, distance and shielding factor need to be

taken in to consideration. Design large room; reduce the time spent with the patient, use

shielding when distance and time are not sufficient, use shield as close as possible to the source.

The source and activity involved need to be considered for shielding calculation. The common

Nuclear Medicine procedures are diagnostic, imaging, PET/CT and hot lab. The shielding issues

are considered for in-vivo measurements, in –vitro measurement and nuclear medicine therapy.

Based on the radionuclide and activity used the hazard in the NM department can be classified as

low hazard, medium hazard and high hazard. The high hazard areas are room for preparation and

dispensing radiopharmaceuticals, Temporary storage of waste, Room for administration of

radiopharmaceuticals, Examination room, Isolation ward. The medium hazard areas are rooms

for storage of radionuclides, Waiting room and Patients toilet. The low hazard areas are rooms

for measuring samples, Radiochemical work (RIA), Offices, Reception. The NM facility should

include fume hood, ventilation, plumbing and first aid.

d) PROCEDURE

The typical layout of nuclear medicine department is shown the figure 1. All the walls are

constructed with 9 inch brick. The floor should have impervious material, washable, chemical-

resistant, curved to the walls and no carpet should be used. Walls should be painted with

washable, non-porous paint (e.g. gloss paint). Worktop surfaces must be finished in a smooth,

washable and chemical-resistant surface with all joints sealed. Cover the work surface with

absorbing papers.

The gamma camera room should have minimum dimension of 30- 40 m2. The room should have

separate control, collimator storage; dose constrains outside the window and shielding to protect

second camera room.



Figure 1: Layout for Nuclear Medicine Department



In hot lab dimension should be minimum 20m2

for 2 isolators/cabinets. Much shielding required

in the hot lab, Hatch to be present, lobby/change area should be available. The injection room

should be adjacent to radiopharmacy and it should be Hatch connected.

Laboratories in which unsealed sources, especially radioactive aerosols or gases, may be

produced or handled should have an appropriate ventilation system that includes a fume hood,

laminar air flow cabinet or glove box.

The fume hood must be constructed of smooth, impervious, washable and chemical-resistant

material. The working surface should have a slightly raised lip to contain any spills and must be

strong enough to bear the weight of any lead shielding that may be required. The air-handling

capacity of the fume hood should be such that the linear face velocity is between 0.5 and 1.0

metres/second with the sash in the normal working position. This should be checked regularly.

The wash-up sink should be located in a low-traffic area adjacent to the work area. Taps should

be elbow operable without direct hand contact and disposable towels or hot air dryer should be

available. An emergency eye-wash should be installed near the hand-washing sink and there

should be access to an emergency shower in or near the laboratory. The sink shall be easy to

decontaminate. Special flushing units are available for diluting the waste and minimizing

contamination of the sink.

There sould be a separate area identified for waste storage.

A separate toilet room for the exclusive use of injected patients is recommended. A sign

requesting patients to flush the toilet well and wash their hands should be displayed to ensure

adequate dilution of excreted radioactive materials and minimise contamination. The facilities

shall include a wash-up sink as a normal hygiene measure. Washrooms designated for use by

nuclear medicine patients should be finished in materials that are easily decontaminated. The

patient washing facilities should not be used by hospital staff as it is likely that the floor, toilet

seat and sink faucet handles will be contaminated frequently.

A separate isolation ward should be provided for I-131 therapy patients (as shown in figure). The

ward toilet should be attached to the delay tank. The typical delay tank layout is shown in Figure

2. The sample is stored for minimum of 4 months in the delay tank and afterwards it is opened to

the public sewerage.

e) RESULTS

The installation planning of nuclear medicine high dose therapy facility was explained.



Figure 2: Delay tank



36. Installation planning of PET-CT scanner

a) AIM

To plan PET-CT scanner installation.

b) REQUIREMENTS

Type of PET-CT scanner, CT workload, Expected PET workload, Max. activity per procedure,

occupancy factor, dimension of the room, calculator, etc,.

c) THEORY

Cyclotron-produced radionuclides are gaining importance in molecular imaging in Nuclear

Medicine departments. The importance of this modality among others is due to the fact that it

provides valuable clinical information, which was lacking in other available modalities.

Presently, every well-established hospital would like to procure Medical Cyclotron or positron

emission tomography-computed tomography (PET-CT) facility in their NM department. The

shielding of positron emission tomography (PET) and PET/CT facilities presents special

challenges. The 0.511 MeV annihilation photons associated with positron decay are much higher

energy than other diagnostic radionuclides. As a result, barrier shielding may be required in

floors and ceilings as well as adjacent walls. Since the patient becomes the radioactive source

after the radiopharmaceutical has been administered, one has to consider the entire time that the

subject remains in the clinic.

Shielding for the CT portion of the PET/CT systems is substantially the same as for any CT

installation. If the PET/CT is used only in conjunction with PET imaging, the CT workload will

be considerably less than that for a dedicated CT system. Because the HVL for the CT

techniques used is so much less than that for 511 KeV photons, a room conservatively shielded

for PET is unlikely to need additional shielding for the CT component.

Factors that affects the amount of shielding required for PET facilities are the number of patients

imaged, the amount of radiotracer administered per patient, the length of time that each patient

remains in the facility, and the location of the facility and its general environs.

d) PROCEDURE

The Typical area for PET-CT facility should be 150-160 sq. m. The most versatile clinical PET

radiopharmaceutical is Fluoro-2-deoxyglucose (F-18 FDG). The calculation has to be performed

based on the administered activity 555 MBq (15mCi) of F18 FDG and there are 40 patients per

week. The uptake time is 60 and the imaging time is 1 hour.



Figure 1: Typical layout for PET-CT scanner installation

e) CALCULATION Radioactive decay Because PET tracers have short half-lives, the total radiation dose received over a time period t ,

D(t), is less than the product of the initial dose rate and time [Ḋ(0) x t].

The reduction factor Rt = D(t)/ [Ḋ(0) x t]

= 1.443 x (T1/2/t) x [1-exp(-0.693t/T1/2)]

For F-18, this corresponds to Rt factors of 0.91, 0.83, and 0.76 for t =30, 60, and 90 min,

respectively.

UPTAKE ROOM CALCULATION

Patients undergoing PET scans need to be kept in a quiet resting state prior to imaging to reduce

uptake in the skeletal muscles. This uptake time varies from clinic to clinic, but is usually in the

range of 30–90 min. The total dose at a point d meters from the patient during the uptake time

(tU) is

D(tU) = 0.092 µSv m2/MBqh x Nw x A0(MBq) x (tU) (h) x RtU/d(m)

2

0.092 µSv m2/MBqh is patient dose rate recommended by AAPM TG108.

Nw – number of patients per week

A0 – administered activity (MBq)

tU – uptake time (h)

RtU – reduction factor



Transmission factor (B) = 10.9 x P x d (m2)/(T x Nw x A0(MBq) x (tU) (h) x RtU)

where (T=1) is the occupancy factor and P is the weekly dose limit in µSv. P=20 µSv for

uncontrolled areas, corresponding to the 1 mSv/ year limit to the general public and P=100 µSv

for ALARA levels in controlled area.

What is the transmission factor required for an uncontrolled area at a point 4m from the

patient chair in an uptake room? Assume patients are administered 555 MBq of F-18

FDG, there are 40 patients per week, and the uptake time is 1 h.

B = 10.9 x 20 µSv x (4)2/ (40 x 555MBq x 1 h x 0.83 = 0.189.

Using Table IV values (AAPM, TG-108), 1.2 cm of lead or 15 cm of concrete shielding is

required.

IMAGING ROOM CALCULATION

If the most conservative approach is taken, where no shielding from the tomograph is assumed,

then the calculation of shielding for the tomograph room is similar to the uptake area calculation.

Because of the delay required by the uptake phase between the administration of the

radiopharmaceutical and the actual imaging, the activity in the patient is decreased by

F(U) = exp-0.693xT(U)min/110, where T(U) is the uptake time.

In most cases the patient will void prior to imaging, removing approximately 15% of the

administered activity and thereby decreasing the dose rate by 0.85. The weekly dose at a distance

d from the source is calculated as

0.092 µSv m2/MBqh x Nw x A0(MBq) x0.85 x FU x (tI) (h) x RtI/d(m)

2

Transmission factor (B) = 10.9 x P x d (m2)/(T x Nw x A0(MBq) x FU(tI) (h) x RtI)

The decay factor for F-18 at 1 h FU is equal to exp(-0.693) x 60/ 110 =0.68.

What is the weekly dose equivalent to a point 3m from the patient during the PET imaging

procedure? Patients are administered 555 MBq of F-18 FDG and there are 40 patients per

week. The uptake time is 60 min and the average imaging time is 30 min.

The weekly dose equivalent

0.092 µSv m2 x 40 x 555MBq x 0.85 x 0.68 x 0.5 h x 0.91/ 3(m

2) = 59.7µSv

What is the transmission factor? (where T=1)

20 µ Sv/59.7 µSv = 0.34.

Using Table IV values (AAPM TG-108), 0.8 cm of lead or 11 cm of concrete shielding is

required.



CALCULATION FOR ROOMS ABOVE AND BELOW THE PET FACILITY

Because the 511keV annihilation photons are penetrating, it is necessary to consider uncontrolled

areas above and below the PET facility as well as those adjacent on the same level. Typically,

one assumes that the patient source of the activity is 1m above the floor. The dose rate is

calculated at 0.5m above the floor for rooms above the source, and at 1.7m above the floor for

rooms below the source.

Figure 2: Distances to be used in shielding calculation

f) RESULTS

The installation planning of PET-CT scanner was explained.



37. Radiation protection survey of nuclear medicine facility

a) AIM

To perform the radiation protection survey at nuclear medicine facility.

b) REQUIREMENTS

Survey meter, contamination monitor, I-131 therapy patients in ward, etc,.

c) THEORY

Nuclear medicine facilities shall be located away from general patient wards and public

occupancy areas. The nuclear medicine facilities shall not be located in residential buildings.

Design and construction of a nuclear medicine laboratory and an isolation ward shall be as per

plan approved by the competent authority.

Active rooms, wards and areas of source storage and handling shall be marked with radiation

symbol and legend denoting the identification of active area and presence of radiation hazard.

Isolation wards shall be provided for patients undergoing nuclear medicine therapy requiring

hospitalization. Areas of high activity and contamination shall be demarcated by physical barriers.

Active areas shall be arranged in increasing order of the activity with entrance provided at the

lowest active area. Walls, floor and doors of the active areas shall have hard, washable, nonporous

and leak-proof covering. Work surfaces shall be covered with nonporous and non-reactive

material.

It is necessary to carry out radiological protection survey of Nuclear Medicine facility to

determine whether it is safe from radiation protection point of view. During the protection survey

radiation levels in and around the installation, at the places occupied by persons and ward are

measured. The radioactive contamination has to be checked periodically at active rooms, fume

hood, L bench, platform, isotope calibrator and waste bin to be free of surface contamination.

d) PROCEDURE

Radiation protection survey: Perform the radiation protection survey at various locations in the

Nuclear Medicine facility using GM survey meter. The layout of Nuclear Medicine department is

shown below.

Measurement of contamination level: Measure the contamination level at fume hood, L bench,

platform, isotope calibrator, waste bin etc., using contamination monitor.



Figure: Typical layout for Nuclear Medicine Department

e) OBSERVATIONS

Survey meter: Contamination monitor: Date of measurement:

Radiation protection survey: Patients administered with 350mCi of I-131 during survey

Name of the

instrument used

Model:

LOCATIONS

(Indicate in Layout Diagram)

A B C D E F G H I J

Exposure level

(µR/h)



Measurement of contamination level

Name of the

instrument used

Sl.No.:

Level of contamination (CPM)

Background Total Net

Fume hood

L Bench

Platform

Isotope calibrator

Waste Bin

f) RESULTS

i) The measured radiation level at various locations is within the acceptable limit.

ii) The measured external surface contamination levels at different locations are within the

acceptable limit.



38. Cross calibration of beam therapy dosimeter

a) AIM

To cross-calibrate the cylindrical or parallel plate ionization chamber used for beam therapy

absolute dosimetry.

b) REQUIREMENTS

Dosimeter to be calibrated, SSDL calibrated dosimeter, water phantom/slab phantom, chamber

adaptor, telecobalt machine, thermometer, barometer, Sr-90 check source, etc.

c) THEORY

The ionization chamber used for beam therapy absolute dose measurement, should have absolute

dose calibration factor. This calibration factor can be obtained from Primary standard laboratory

(PSDL) or secondary standard laboratory (SSDL). The PSDL have primary standard dosimeters

like FAC, Calorimeter, graphite chamber etc. The SSDLs obtain calibration factor for their

instruments from the primary standard laboratory. These instruments are called secondary

standard dosimeters. The user instruments (dosimeters used in hospital) are mostly calibrated

against the secondary standard dosimeters. In our country, we have SSDL, at BARC. The user

may have many dosimeters for beam therapy absolute dosimetry. It may not be possible to

calibrate all the instruments at SSDL. One dosimeter may be calibrated at SSDL, based on that,

the user can cross-calibrate other instruments using their teletherapy beam.

Cross calibration of field ionization chamber:

The instrument calibrated at SSDL is known as reference dosimeter and the instrument to be

calibrated is known as field dosimeter. The field chamber (either cylindrical or plane-parallel)

may be cross-calibrated against a calibrated reference chamber in a 60

Co beam at the user

facility. The chambers are compared by alternately placing each chamber in a water

phantom/slab phantom with its reference point at z in accordance with the reference conditions;

this is known as substitution method. A side by side chamber inter comparison is also possible

this is known as simultaneous method. The calibration factor in terms of absorbed dose to water

for the field ionization chamber is given by

where Mref and Mfield are the meter readings per unit time for the reference and field chambers,

respectively, corrected for the influence quantities and Nfield

D,w is the calibration factor in terms

of absorbed dose to water for reference chamber.

d) PROCEDURE

The following procedures need to be followed for calibration of field instruments. 1) Check the

instrument for working condition, 2) Check for natural leakage (Pre-irradiation leakage), 3) Pre-

irradiation dose to the chamber, 4) post irradiation leakage (radiation induced leakage), 5) stem-



effect, 6) Absolute dose calibration (substitution or simultaneous method), 6) Linearity check, 7)

stability check with Sr-90 check source.

1) Instrument working condition: Switch on the instrument in the telecobalt room, check for

working condition. Place the chamber in the treatment room, at least 30 min before the

measurement to settle down to environmental condition.

2) Check for natural leakage: The natural leakage can occur in the instrument in the absence of

radiation field. The large leaks may occur due to dirty connectors, wet desiccators, not giving

instrument long enough to settle, not giving a pre-irradiation dose to the chamber. To test the

natural leak after the instrument has been setup, start the electrometer and watch the reading

for a period of time similar to that for which a normal reading would be taken. Stop and

record the reading and repeat 3 times, if the drift is more it should be accounted for correcting

the actual reading.

3) Pre-irradiation dose to the chamber: The pre-irradiation dose to the chamber known as

radiation bath should be given to the chamber for minimum of 5 min to clear the natural

leakage and residual charges.

4) Radiation induced leakage: A radiation induced leakage is associated with the chamber and

is identifiable only after the chamber has been exposed to a radiation field. After ir-radiation

leave the instrument for few minutes without re-set. If radiation induced leakage is present,

there is usually a continued collection of charge even after the beam has been switched off, at

a similar rate to that of the reading. Radiation induced leaks vary in their magnitude may be

ignored, provided they are small. If chamber leakage is more, it requires repair by the

manufacturer.

5) Stem effect: When using a cylindrical chamber, the charge collection efficiency may also get

affected due to irradiation of stem portion of chamber. The influence of this factor should be

less than 0.5%.

6) Substitution method: Place the reference chamber in water phantom at 10 cm depth using

10cm x 10 cm field size, SSD=80, Reference point of the chamber, for cylindrical chambers,

is on the central axis at the centre of the cavity volume. For plane-parallel chambers, it is on

the inner surface of the window at its centre with the beam. Note down the meter reading

(Mref), maintain the same measurement condition, replace the reference chamber with the field

chamber and note down the meter reading (Mfield).

7) Linearity check: Note down the meter reading for field dosimeter for different exposure times

of 0.5 min, 1min, 2min, 3min, 4min, etc,. Check the linear response of meter reading. Plot the

graph of time versus response.

8) Stability check with Sr-90 check source: Place chamber inside the Sr-90 check source hole

provided. Find out the time to reach the particular meter reading using stop watch. Note down

the stop watch reading for at least 10 measurements. Note down pressure & temperature by

placing the thermometer inside the hole to account for air density correction.



e) OBSERVATIONS

Field instrument: Type: Chamber:

Reference instrument Type: Chamber:

Calibration Conditions:

SSD: Field Size: Depth:

Polarizing voltage: Mode:

Reference condition: 20 c, 1013.2 mbar at standard STP.

Temperature (T): Pressure (P):

Pre- irradiation dose to the chamber (Radiation bath) for 5 min

Check for natural leakage:

Sl.No. Pre-irradiation Meter

reading observation

for 3 mins

1

2

3

Radiation induced leakage:

Sl.No. Post-irradiation Meter

reading observation

for 3 mins

1

2

3

Stem effect

Sl. No. Meter reading with 5x16

field size

Meter reading with 16x5

field size

1

2

3

Average

Variation of meter reading with reference to field size: %



Substitution method

Exposure for ________min

Sl.no Meter reading for

reference dosimeter (Mref)

Meter reading for

field dosimeter(Mfield)

1

2

3

4

5

Average

Absorbed dose to water calibration factor for reference dosimeter

ND,wref

= Gy/C

Absorbed dose to water calibration factor for field dosimeter

ND,w

field = Gy/C

stability check with Sr-90 check source:

Model of Sr-90 Check source:

Temperature(T): Pressure (P):

Meter reading observed for the time ‘t’: ___________

Sl. No. Time for observed

meter reading (Sec) (R)

1

2

3

4

5

6

7

8

9

10

Average

(A)



Corrected time air density correction (M) = A X (P/1013.2) x (293.2/(273.2+ T)

=

Standard deviation (S) = (√Ʃ(Ri-M)2)/ (√(n-1))

Where n is the number of observations.

Standard uncertainty of the mean (U) = S/√n

f) RESULTS

The absorbed dose to water calibration factor for the field instrument (ND,w) is _________.



39. Calibration of survey meters using Cs-137 source

a) AIM

To calibrate the survey meters using Cs-137 source.

b) REQUIREMENTS

Survey meter, Cs-137 source, calibration jig, long forceps, etc.,

c) THEORY

Survey meters (Radiation monitoring instruments) are portable, battery operated and generally

measure exposure or exposure rate. Calibration of these instruments are usually done by the

manufacturer. However, due to many factors such as changes in detector insulation, climatic

effect on components etc. the original calibration ceases to be valid. Therefore in order to get the

accurate readings it is essential to re-calibrate the instruments time to time. The response of the

detector has to be checked with the help of standard radioactive source, whose exposure rate at

various distances can be calculated. It is also necessary to check the response of the instrument

for the various energies of radiation expected to be encountered.

The exposure rate at various distance from the source (X) = (Γ X A)/d2 mR/hr

where Γ – specific gamma ray constant for the source (Rm2hr

-1mCi

-1)

A – Activity of source (mCi)

d – detector distance from the source (m)

The calibration factor for the radiation monitor

= Measured exposure rate/calculated exposure rate.

d) PROCEDURE

Place the survey meter at a distance„d‟ from the source. Note down the meter response and

compare it with calculated exposure rate. Repeat the measurement for other distances. Tabulate

the reading and find out the calibration factor.



Figure: experimental setup for survey meter calibration

e) OBSERVATIONS

Source used: Cs- 137

Activity : mCi

Specific gamma ray constant: 3.26 Rcm2hr

-1mCi

-1

Calculated exposure rate__________mR/hr at ________distance.

Sl. No. Range Observed reading

(mR/hr)

Calibration

Factor

f) RESULTS

The survey meter is calibrated using Cs-137 standard source.



40. Procedural aspects of transport of Radioactive Material used for

Teletherpay and Brachytherapy

a) AIM

To understand the regulatory procedure (obtaining licence) involved in import and export of

teletherapy and brachytherapy sources.

b) REQUIREMENTS

Regulatory form like REV.5, RT-COM, RT-STREPORT, UT-COM, RT-ATH, RT-SSA, UT-

ATH, eLORA system etc.

c) THEORY

It is mandatory to obtain the Atomic Energy Regulatory Board (AERB) licence to import and

export (dispose) the teletherapy and brachytherapy sources. The request forms need to be

submitted to AERB. Currently AERB recommends use of eLORA for obtaining the import and

export licence.

d) PROCEDURE

Teletherapy source import licence: To obtain the import licence for teletherarpy source the

following forms need to be submitted to AERB.

1) Quotation or source purchase receipt from the supplier and also quotation for disposal of

decayed old source.

2) APPLICATION FOR AUTHORISATION TO PROCURE RADIATION SOURCES

FOR RADIATION THERAPY. AERB/RSD/RT/ATH - This form provides information

about available staff and equipment details, source specification and activity to be

purchased.

3) UNDERTAKING REGARDING THE PERFORMANCE EVALUATION OF THE

RADIATION THERAPY UNIT FOR OBTAINING AUTHORISATION.

AERB/RSD/RT/UT-ATH – for re-loading source in the existing unit, this form need to

be submitted.

4) APPLICATION TO AUTHORIZE MEDICAL PHYSICIST/RADIOLOGICAL SAFETY

OFFICER FOR SUPERVISION OF SOURCE TRANSFER OPERATION IN

RADIOTHERAPY. AERB/RSD/RT/SSA

5) Information on transport of radioactive material for disposal. AERB/RSD/TP-DISP-Q-1/REV.5- If unit is having decayed source, to obtain authorization for disposing decayed source this form need to be submitted.

The teletherapy source is normally transported through the source flask. Along with the source flask, the user may receive the following documents a) Trem card b) Consignor details

c) Consignee details

d) Consignor declaration

e) Transport index

f) Max. radiation level on the external surface of the package.



g) Type of package [type B(U), III Yellow]

After source transfer, the following forms need to be submitted to AERB to obtain treatment

commissioning approval.

6) APPLICATION FOR COMMISSIONING OF RADIATION THERAPY FACILITY.

AERB/RSD/RT/COM – This form provides information about available staff and

equipment details.

7) REPORT ON SOURCE TRANSFER/DECOMMISSIONING OF

TELETHERAPY/BRACHYTHERAPY FACILITY. AERB/RSD/RT/ST-REPORT

8) UNDERTAKING REGARDING THE PERFORMANCE EVALUATION OF THE

RADIATION THERAPY UNIT FOR COMMISSIONING APPROVAL

AERB/RSD/RT/UT-COM

QA has to be performed as per RPhD/Telegamma/QA/95 protocol and record should be

maintained for regulatory inspection.

Brachytherapy source import licence: To obtain import licence for brachytherapy source

the following forms need to be submitted to AERB. a) Concern from the supplier to take back decayed source.

b) APPLICATION FOR AUTHORISATION TO PROCURE RADIATION SOURCES FOR

RADIATION THERAPYAERB/RSD/RT/ATH – provides information about institute,

equipment and staff details.

c) PROCUREMENT OF REMOTE AFTERLOADING BRACHYTHERAPY SOURCE

FORM-AERB/RT/RAL - provides information about source specification, supplier,

equipment, etc.,

d) UNDERTAKING REGARDING THE PERFORMANCE EVALUATION OF THE

RADIATION THERAPY UNIT FOR OBTAINING AUTHORISATION.

AERB/RSD/RT/UT-ATH.

QA has to be performed as per RP&AD/Remote QA/01 protocol and record should be

maintained for regulatory inspection.

Brachytherapy source export licence: To obtain export licence for brachytherapy source

the following forms need to be submitted to AERB. a) Information on export of radioactive material. AERB/RSD/TR-DISP-Q-1/REV.5. This

form provides information about supplier, specification of the source, package details, transport index, Max. radiation level on the external surface of the package, mode of transport, etc,.

e) RESULTS The regulatory procedure involved in the transport of teletherapy and brachytherapy sources were understood.



REFERENCES

1. Acceptance/Quality Assurance Tests for Telegamma Therapy Unit.

RPhD/Telegamma/QA/95.

2. Acceptance/quality assurance tests for medical linear accelerator. RPAD/ACC/QA/04.

3. Faiz M Khan. The Physics of Radiation Therapy, 4th

edition. Lippincott Williams &

Wilkins. 2010.

4. International Atomic Energy Agency. Technical Reports Series No. 398. Absorbed Dose

Determination in External Beam Radiotherapy. Vienna: International Atomic Energy

Agency; 2000.

5. Jacob Van Dyk, The modern technology of radiation oncology. A compendium for

Medical Physicists and Radiation Oncologists, Medical Physics Publishing, Madison,

1999.

6. Madsen et al. PET and PET/CT Shielding Requirements. AAPM Task Group 108, Med.

Phys. 33(1), January 2006.

7. Proforma for acceptance / quality assurance tests of remote afterloading brachytherapy

unit. RP&AD/Remote QA/ 01, 2001.

8. Radiation therapy sources, equipment and installations. AERB SAFETY CODE NO.

AERB/RF-MED/SC-1 (Rev.1). 2011.

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