preface beam data collection and commissioning for linear

AAPM-SAM-2012-Das (1)

IDas/AAPM/2012

Indra J. Das, PhD, FAAPM, FACR, FASTROIndra J. Das, PhD, FAAPM, FACR, FASTRODepartment of Radiation OncologyDepartment of Radiation OncologyIndiana University of School of Medicine & Indiana University of School of Medicine & Indiana University Health Proton Center Indiana University Health Proton Center IndianaIndiana

Beam Data Collection and Commissioning for Beam Data Collection and Commissioning for Linear Accelerators: Technical Considerations Linear Accelerators: Technical Considerations

and Recommendationsand Recommendations

IDas/AAPM/2012

PrefacePreface

Med. Phys. 35(9), 4186-4214, 2008 IDas/AAPM/2012

IDas/AAPM/2012

2008IDas/AAPM/2012

Mechanical QA

CollimatorCollimatorTableTable GantryGantry

4Qudrant Independent Jaw Test

Radiation Survey

Mechanical tests

Light radiation

Table, Collimator, Gantry

Jaws

MLC

Imaging parameters

Other as TG-142

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Planning for Commissioning Data


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Time= [(PDD + 5 profiles)/beam energy]x ( open + 4 wedges) x 60 points/scanx [(1 s/pts + (1s/movement and delay)]x (15 fields x 2 energies)

∼105 s∼ 30 h

Planning for Commissioning TimePlanning for Commissioning Time

IDas/AAPM/2012

Rational For Commissioning Beam DataFirst, it is not evident that manufacturing procedures for all linear accelerators have produced a level of reproducibility acceptable for clinical use. For example, variations in beam parameters have been noted between beams with the same nominal energies.

Second, on-site changes made during installation and acceptance of the user’s accelerator e.g., changes in beam energy and/or profiles from beam steering will not be modeled in the golden data.

Third, the beam characteristics of the soft wedges are made by moving jaws that depend on the speed parameters of the jaws and a deviation at site could affect the beam profile of the soft wedge.

Fourth, although acceptable agreement with the golden data set may be found in individual checks, it may be that some clinical setups will have multiple errors, which combine to produce unacceptable results.

TG-106

IDas/AAPM/2012

Hrbacek, et al Med. Phys. 34, 2917–2927, 2007.

Rational For Not Using Golden Data

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Hrbacek, et al “Quantitative evaluation of a beam-matching procedure using one dimensional gamma analysis,” Med. Phys. 34, 2917–2927, 2007.

Rational For Not Using Golden Data

|xi − x¯ | <Δ, � xi

Δ =? (0.5, 1.0 0r 2%)

IDas/AAPM/2012

Standard chamber 10−1 cm3—The active volume for a standard Farmer-type ionization chamber is on average 0.6 cm3.Minichamber 10−2 cm3—The active volume for a mini-ionization chamber is on average 0.05 cm3.Microchamber 10−3 cm3—The active volume for a microionization chamber is on average 0.007 cm3

and ideally suited for small field dosimetry such as radiosurgery,gamma knife, CyberKnife, and IMRT

Definition of Detectors

IDas/AAPM/2012

Water

Air

1 2 3 4 5

Setting Water Tank & DetectorSetting Water Tank & Detector


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Know Your Connectors

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Understand Detector, Connector & CableUnderstand Detector, Connector & Cable

Srivastava et al, SU-GG-T-270, 2010

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Quality of Cables

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Setup and Possible Errors

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ElectrometerNull SettingCable subtractionProper bias

>300 V for ion chamber100 V for diamond0 v for all diodes

Proper gainProper mode

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Choose Consistent & Correct Polarity


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Chambers & Gain

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Selection of detector for beam data

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XYZ

XY

Z

Scan Direction

Chamber Orientations

Radiation beam

Choice of Detector OrientationChoice of Detector Orientation

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Detector Orientation

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0102030405060708090

100110

0 0.5 1 1.5 2

Rel

ativ

e Dos

e

Distance Off Axis (cm)

6MV, 2x2 cm2 field, Illustration of chamber volume effects

Diode, dmax

PTW Pinpoint, dmax

RK chamber, dmax

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0

50

100

150

200

250

-20 -15 -10 -5 0 5 10 15 20

Rel

ativ

e D

ose

Distance Off Axis(cm)

6 MV 60 Deg Wedge, 10 cm depth: water vs Profiler

Diode Array Profile

Water Profile

IDas/AAPM/2012

0

20

40

60

80

100

120

140

160

180

200

-20 -15 -10 -5 0 5 10 15 20

Rel

ativ

e D

ose

Distance Off Axis(cm)

18 MV 60 Degree Wedge, 10 cm depth, 100 cm SAD: Water vs Profiler

Diode Array profile

Water Profile

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Scanning Speed

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Scanning Speed

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0

20

40

60

80

100

0 5 10 15 20 25 30 35

Perc

ent D

epth

Dos

e

Depth(cm)

Arithmetic Mean (AM) smoothing: 60 Degree Wedge PDD

UnsmoothedAM x 1AM x 2AM x 3AM x 5

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IDas/AAPM/2012

Future of Beam Data Commissioning

Standardization of linear acceleratorsMonte Carlo based commissioningNewer Radiation Detectors & CablesNewer Scanning SystemsSmart algorithms

IDas/AAPM/2012

Aubin et al., Med Phys, 37(5), 2279-2288, 2010IDas/AAPM/2012

Monte Carlo Codes

Aubin et al., Med Phys, 37(5), 2279-2288, 2010

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Simulation of intensity at target


Simulated Profiles


Profiles for different fields


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Depth Dose Simulation


Detector Manufacturer Type volumeSFD Scanditronix Photon diode 1.7x10-5cm3

PFD Scanditronix Photon diode 1.9x10-4cm3

Exradin A-16 Standard Imaging Ion chamber 0.007cm3

Wellhofer-IC4 Scanditronix Ion chamber 0.40 cm3

Pinpoint PTW Ion chamber 0.015cm3

0.125cc PTW Ion chamber 0.125cm3

0.3cc PTW Ion chamber 0.3 cm3

0.6cc PTW Ion chamber 0.6 cm3

Diamond PTW Diamond 0.003cm3

Markus PTW Parallel plate 0.055cm3

Edge Detector Sun Nuclear Diode 10-5cm3

Other

Detectors

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Sensitivity vs Volume of Detectors

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00

Volume (cm3)

Rel

ativ

e se

nsiti

vity

PFD

SFD

A-16 PinPointMarkus

IC4

0.125cc

0.3cc

0.6 cc

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Treatment FieldsMagna-Fields

Traditional Fields

Advance Therapy FieldsSRS/SRTGamma KnifeCyber-KnifeTomotherapyIMRT

40x40 cm2 4x4 cm2

4x4 cm2 0.3x0.3 cm2

200x200 cm2

Small Field

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What is a Small Field?Lack of charged particle

Dependent on the range of secondary electronsPhoton energy

Collimator setting that obstructs the source sizeDetector is comparable to the field size

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Views of Source Sizes

Jaffray et al, Med Phys 20, 1417-1427 (1993).


IDas/AAPM/2012Das et al, Med. Phys. 35, 206-215, 2008

Definition of Small Fields

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For each element, find the contributions from the relevant sources

Calculation of Fluence Map Elements

Raytrace to calculate attenuationor use approximate penumbra shape

The width and shape of the source

POI-eye-view of the source!

Dominating effect:

Courtesy Ahnesjö IDas/AAPM/2012

Dosimetry

AbsoluteDose

RelativeDepth Dose [D(r,d)/D(r,dm)]TMRProfilesOutput, Scp (total scatter factor), [D(r)/D(ref)]

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6 MV; Central Axis

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

0 1 2 3 4 5 6 7 8 9 10 11

Field Size (cm)

Rel

ativ

e do

se a

t dm

ax

Scanditronix-SFDScanditronix-PFDExradin-A16PTW-PinpointPTW-0.125ccPTW-0.3ccPTW-0.6ccPTW-MarkusWellhofer-IC4

15 MV; Central Axis

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

0 1 2 3 4 5 6 7 8 9 10 11

Field Size (cm)

Rel

ativ

e do

se a

t dm

ax

Scanditronix-SFDScanditronix-PFDExradin-A16PTW-PinpointPTW-0.125ccPTW-0.3ccPTW-0.6ccPTW-MarkusWellhofer-IC4

Field Size Limit for Accurate Dose Measurements with Available Detectors

Das et al, TG-106, Med Phys, 35, 4186, 2008

IDas/AAPM/2012

Relative Dosimetry

refmsr

msr

msr

msr

msr

msr

,,,,,

ffQQQoQQoDW

fQ

fQw kkNMD =

( ) ( )( ) ( )

msrclin

msrclinmsr

msr

clin

clin

msr

msr

msr

msr

clin

clin

clin

clin

msr

msr

clin

clinmsrclin

msrclin

,,

,w

,w

// ff

QQfQ

fQ

fQ

fQ

fQ

fQ

fQ

fQff

QQ kMM

MDMD

MM

=⎥⎥⎦

⎤

⎢⎢⎣

⎡=Ω

msrfmsrairw

fclinfclinairwffQQ PS

PSk msrclin

msrclin ⋅⋅

=)()(

,

,,,

( ) ( )( ) ( ) rel

relf

Qf

Q

fQ

fQff

QQ adingOutput

MDMD

k msrclin

msrclin )(Re)(

//

clin

msr

clin

msr

clin

clin

msr

clin

,w,w

,w,w,, ==

IDas/AAPM/2012

New Data on Correction Factor

Pantelis et al, Med Phys, 37(6), 2369-2378, 2010


IDas/AAPM/2012

0.90

0.92

0.94

0.96

0.98

1.00

1.02

1.04

1.06

1.08

1.10

1.12

1.14

1.16

0 5 10 15 20 25 30 35

Field size (mm)

Cor

rect

ion

fact

or

Siemens; PTW diode 60012Elekta; PTW diode 60012Siemens; Exradin A16Elekta; Exradin A16Siemens; Sun Nuclear Dedge"Elekta; Sun Nuclear Dedge"Siemens; PTW Pinpoint 31014Elekta; PTW Pinpoint 31014Siemens; PTW microLionElekta; PTW microLion

msr

clin

msr

clin

, ,ff

QQk

msrclin

msrclin

,,ffQQk

IDas/AAPM/2012 Chung et al, Med Phys, 37(6), 2404-2413, 2010

New Data on Correction Factor

IDas/AAPM/2012

kQ is not Constant in Small Field

Kawachi et al, Med Phys, 35, 4591-4598, 2008

IDas/AAPM/2012Sham et al, Med Phys, 35, 3317-3330, 2008

Depth Dose & Source Size

IDas/AAPM/2012

Profile & Source Size

Sham et al, Med Phys, 35, 3317-3330, 2008 IDas/AAPM/2012

Comparison of Large Tank and Small SRS Cylinder Tank for SRS, TMR & Profiles

ARM Inc., Port Saint Lucie, FL 34983ARM Inc., Port Saint Lucie, FL 34983

Moving Tank System for TMR


IDas/AAPM/2012

No SSD to SAD calculations required, No cubic No SSD to SAD calculations required, No cubic splinespline fit of a fit of a limited number of fixed data points neededlimited number of fixed data points needed

Calculated TPR ~2% less at depth Cubic spline fit of 12 data points

NikeschNikesch et al, CyberKnife Center , Palm Beach, FLet al, CyberKnife Center , Palm Beach, FL

Direct TMR Data AcquisitionDirect TMR Data Acquisition

IDas/AAPM/2012

3D Scanner (Sun Nuclear)Setup Subjectivity

Automatic leveling, water surface detection and beam center detectionNo tank shifts

Detector orientation/resolution3D Scanner design always using the short dimension of chamber to scan

TimeSetup is faster and more accurateNo tank shiftsSmaller tank fills and drains faster

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Scanner Orientation Advantage

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Sun Nuclear 3D Scanner

2

1

1

32

1. Ring drive maintains consistent scanning direction

2. Diameter drive has maximum scanning range of 640mm

3. Vertical drive has maximum travel of 400mm IDas/AAPM/2012

ConclusionsGolden Data should be taken as a reference onlyUnderstand time and amount of data to be takenView each parameters properly, double check by another individualUse proper detector for each type of data collectionSet optimum speed for scanning, do not rush

IDas/AAPM/2012

-Conclusions

Understand the limits and measuring conditionQuestion every unusual data setDo not smooth data too muchWrite report for future referenceFuture technology & resources could help commissioning simpler


IDas/AAPM/2012

ThanksThanks

preface beam data collection and commissioning for linear

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