idos 2019 symposium highlights · •trs 398 ⎼a plenary session describing the status of the...

IDOS 2019

Symposium highlights

Saiful Huq

AAPM

Thank you

IDOS-2019 concluding session 2

• Penelope Allisy-Roberts

• Yuni Dewaraja

• David Followill, Stephen Kry, Paige Taylor &

Daniela Branco

• Cecilia Kessler

• Ferid Shannoun

• Rodolfo Cruz-Suarez

• Ahmed Meghzifene

Half a century of IAEA radiation

dosimetry developments


The IAEA efforts for the developments of radiation

dosimetry during the last 50 years were highlighted

in the opening session

• Guidance and Codes of Practice on dosimetry, first on RT

and extended to DR and NM

• Support to Member States for setting up SSDL

infrastructure & medical physics

• Provision of dosimetry services (IAEA Lab)

• Harmonization of education and clinical training

Dosimetry audits in radiotherapy: past,

present and future


This session highlighted the past 50 years of

accomplishments and developments of dosimetry audits by

IAEA and IROC-Houston: from having no dosimetry

standards in the late fifties to the development of many

standards and audit programs to harmonize reference and

clinical dosimetry across SSDLs and clinical practices

Audits of new technology in current

clinical practice


• IROC-Houston’s QA center discussed their

comprehensive remote and on-site dosimetry audit

program for proton therapy

• NRCC gave an update of their efforts to develop

programs using alanine as a remote dosimeter for postal

audit of clinical programs

• MD Austran reported on their collaborative dosimetry

audit based on end-to-end testing with alanine in proton

beam therapy

• Japan reported on their external QA audits of carbon-ion

RT for multi-institutional clinical trials

Small field dosimetry


• IAEA and AAPM jointly published a new Code of Practice

on Small Field Dosimetry – TRS483

• A topical session on this highlighted the results of the

testing of this CoP through the work of a CRP formed by

IAEA in 2015

• Initial results of the work of the CRP members show that

implementation of the recommendations given in TRS 483

harmonizes dosimetry of small fields



The topical session also highlighted the following:

• An IAEA initiated pilot study of an audit program for small

photon beams using a newly designed phantom. Results

of this study provided validity of the audit program

• New data for output correction factors for ionization

chambers currently in clinical use but not included in

TRS483

• Presentation on how to perform reference dosimetry on a

new biology guided device that has small reference field

size



• Testing of the recommendations of TRS483 using plastic

phantoms and 2D detector arrays

• A presentation outlining the choice of an appropriate ion

chamber or diodes for measuring depth dose curves for

small field sizes in the build up region

• A presentation on the implementation of plan-class-

specific reference field concept using multidimensional

clustering of plan features. The findings indicated that

there were no intuitive plan clusters and that it might be

more useful to consider corrections on a case by case

basis

Computational dosimetry


• A presentation on the construction of an Al calorimeter

and an Al cavity chamber to determine the values of Wair

was given. Plans are underway to undertake various

experiments to study the energy dependence of Wair

• The impact of different models in the calculation of

Compton mass energy-transfer coefficients was

presented. The need to use normalized photoelectric

cross sections in the calculations was highlighted

• NPL presented the MC calculated conversion and

correction factors for its HDR Ir-192 brachytherapy

absorbed dose to water standard and measured dose

rate constant for the HDR Ir-192 Flexisource

International dosimetry framework and

traceability


The following was highlighted:

• Background and establishment of the international

measurement system and the important roles of the

BIPM, PSDLs and CIPM-MRA

• The background and functions of the international

Consultative Committee for Ionizing Radiation (CCRI).

• The importance of working collaboratively to support

each other internationally in terms of the access and use

of radiation sources for metrology

• The important role of the IAEA/WHO SSDL Network in

the dissemination of standards to SSDLs

International dosimetry framework and

traceability


• The need for cooperation between the SSDLs and the

end users; pointing out that the DOLNET database

serves as the focal information interface for this purpose

• The IAEA-SSDLs comparisons can be used to support

the calibration and measurements capabilities of selected

participating SSDLs

Development of Primary Standards


• A primary standard for absorbed dose to water was

developed for radiopharmaceutical therapy, allowing

determination of Dw based on direct measurements rather

than using tabulated nuclear data. The standard is based

on a conventional extrapolation ionization chamber and

MC calculations to evaluate correction factors

• A “mini” graphite calorimeter was developed to determine

absorbed dose in small fields of high energy photon

beams


IDOS-2019 Concluding session 13

• A primary standard, based on a brass wall spherical

ionization chamber, was developed by NIST for air kerma

determination of a 6 MV photon beam for security purposes.

• Fricke dosimetry can be used as a primary standard for

HDR Ir-192 source, together with MC calculations to

determine absorbed dose

• Air attenuation correction for free air chambers is currently

based on measurements. MC values of air attenuation differ

significantly from the measured values. These calculated

values are in closed agreement with the measured values if

the renormalized photoelectric cross-sections for low-

energy x-rays are used, as recommended by the ICRU 90



• Proton dosimetry: a graphite calorimeter was developed at

the NPL to be used in clinical proton beams. The dose

obtained using the graphite calorimeter are consistent

within the uncertainties when compared to the dose

derived using the TRS 398 CoP, but with improved

uncertainties

Updates on reference dosimetry


• TRS 398

⎼ A plenary session describing the status of the update of

TRS-398 CoP was given. Numerous developments since

the publication of TRS-398 necessitates an update.

Updated data will be given for all beam types. For photon

beams, no significant difference is expected between the

data given in TRS-398 and those to be included in the

update. The hope is to publish the update within the next

2-3 years

Reference dosimetry- additional updates


• Progress toward updating the TG-51 protocol for electron

beam reference dosimetry was presented

• The aim is to improve the accuracy of beam calibration by

providing updated beam quality conversion factors and

simplifying the calibration procedure (e.g., by removing the

requirement for a measured gradient correction) with the

goal of reducing errors in the clinic

Dosimetry in nuclear medicine


• Model based vs. patient specific dosimetry and its

implications on nuclear medicine dosimetry

• Several aspects of cell level dosimetry

• Outcomes of the MRT dosimetry project, aiming at providing

an open access database of reference images (phantom

measurements and MC simulations), to be used as reference

data for commissioning and QC of SPECT/CT quantitative

imaging



• Clinical alpha particle dosimetry: its promises and the use of

imaging/dosimetry results to optimize therapy

• Adaptive biological treatment planning

• Parametric optimization of predictive mathematical model for

the final thyroid mass determination, assuming heterogeneity

of thyroid gland mass density

• Patient specific dosimetry in radiosynovectomy



A panel discussion on whether patient specific

dosimetry in NM improves patient care? Interesting

discussion indicated that clinical dosimetry is

lacking because

⎼ Time and resources are needed for dosimetry

⎼ Uncertainty in calculation

⎼ Lack of evidence

⎼ Resistance by authorities not to exceed 23 Gy limit to

the prescription dose

⎼ Lack of insurance coverage in some countries

Out of field dosimetry


• EURADOS WG9 reported assessment of out of field

dosimetry for pediatric radiotherapy patients for various

photon beam treatment techniques

• A semiconductor probe was modeled for out of field MC

dose calculations. Good agreement was obtained between

in-field dose calculations and validation measurements.

Out of-field calculations were found to be in good

agreement with published data

• Evaluation of out of field doses given to patients from

various on board imaging systems attached to the

accelerator were presented. Emphasis was given to be

cognizant of added radiation dose from imaging

Out of field dosimetry


• Efficacy for using OSLD for in-vivo out of field dosimetry

was investigated with the suggestion that OSLD might not

be the detector of choice for out of field dosimetry

• Calculations of organ neutron doses from accelerators

showed that the flattening filter composition caused the

greatest changes in neutron dose

Protons and beyond


• There are currently 73 proton therapy facilities and 11

carbon facilities in operation worldwide

• ICRU is preparing a report on Prescribing, Recording, and

Reporting Light Ion Beam Therapy (Report 93), updating

and expanding the ICRU 78 report. The main

recommendations include the disuse of Gy(RBE), to be

replaced with just Gray (Gy). For dose reporting, physical

dose, RBE-weighted dose, and LET distributions should all

be recorded

• The effect of the ICRU 90 report on kQ factors for carbon

beam calibration

• A primary standard for protons is being developed by NPL,

based on a graphite calorimeter

Protons and beyond


• Results of an ion chamber inter-comparison in several

proton beams was reported . Ion recombination was

compared in a low-energy passive scattered beam using

the two-voltage method, which underestimated the

recombination. Measured data agreed within 1.2%, but

measured vs. TPS data showed discrepancies up to 3.1%

• Alanine can be used as a dosimeter for ion therapy, but a

correction factor is necessary to account for variable

stopping powers of each particle (primary and secondary

particles) in alanine

• Proton reference dosimetry for scanning proton beams, in

terms of number of particles or dose area product (DAP)

• A large-area ion chamber or a PTW Roos chamber can be

used to calibrate monitor chambers in a synchrotron

Dosimetry as a tool for optimization and

auditing


• The importance of optimization was highlighted through

several examples in clinical practice

• Dose management systems are useful in the speedy

evaluation of patient dose, from DAP readings and the

measured reference air kerma rate

• Bismuth shielding of 1 mm over the neck reduces thyroid,

eye lens and other organ doses by as much as 60 % during

CT of the cervical spine, without loss of diagnostic

information, although the images were slightly (1%) more

noisy

Dosimetry as a tool for optimization and

auditing


• The IAEA/ICRP project to reduce lung and thyroid doses in

paediatric chest CT through the use of optimized clinical

protocols was highlighted. Dose savings of 25 % for the lung

and 13% for the thyroid were achieved with radiological

acceptable CT images

Dosimetry for radiobiology


• No CoP for dosimetry of kV X rays used for radiobiology

research

• Dose verification survey (NIST) of gamma and X-ray

irradiators revealed large deviations in output

measurements

• No dedicated CoP for dosimetry for radiobiology research

• NPL works on the development of recommendations for

the dosimetry of in-vitro radiobiology experiments for

medium energy X rays

Monte Carlo in Diagnostic Radiology and

Nuclear Medicine Imaging


MC in Diagnostic Radiology

• MC for reference dosimetry for: diagnostic and

interventional radiology, benchmarking, deriving dose

conversion coefficients from anatomical phantom, kV

spectra and design of X-ray tubes

• Independent calculations of Bw for a broad range of x-ray

beam qualities and field sizes using MC were presented

MC in Nuclear Medicine

• MC codes used for dosimetry, SPECT and PET imaging

• Use MC voxel-level dosimetry only if needed. For simple

geometries and homogeneous tissue use point kernel

convolution and local energy deposition

Monte Carlo in Diagnostic Radiology and

Nuclear Medicine Imaging


• The OpenDose project brings together resources and

expertise through an international collaboration to generate,

verify and disseminate reference dosimetric data to the

Nuclear Medicine community. A web interface to allow free

access to the database will be online soon

• Dose Optimization System and Integrated Software

(DOSIS): a patient-specific MC based dosimetry toolkit is

being benchmarked with other validated MC codes and

showed good agreement

Black box dosimetry


• Black box solutions will most likely prevail in the future

• Black box solutions can improve RT services, but can

constitute a risk when implementation is carried out by

under-trained professionals

• A medical physics perspective on the Halcyon ( as a black

box solution) was presented and highlighted the need to

assess the suitability of Halcyon for LMI countries

Novel dosimetry


Presentations focused on

• Challenges and potential solutions of Ion-recombination

effects associated with ultra-short high dose-per-pulse in

very high energy electron beam at CERN and in a clinical

accelerator

• Nanodosimetric track structure analysis for estimating

RBE variations in a clinical proton beam. Results for

predictive variations of RBE for lethal lesions in cells

were encouraging

Novel dosimetry


• Study by EURADOS WG to asses varying models of

cross-sections data on the uncertainty of micro-

dosimetric data

• Evaluation of a novel semiconductor chip capable of

recording spectral information to make more accurate

dose measurements. Promising results were obtained

with the diode showing greater detection efficiency.

Further developments and testing are needed for clinical

implementation

Dosimetry in the presence of magnetic

fields


Session focused on development of new

calorimeters and simulation of ion chambers for

measurement of absorbed dose in the presence of

magnetic fields and development of dosimetry

audits for MR linacs: Example:

• Design of a new water calorimeter for the measurement of

absorbed dose in an MR linac; this will allow direct

calibration of ionization chambers for use in the presence

of magnetic fields

Dosimetry in the presence of magnetic

fields


• Design and manufacture of an ion chamber shaped

graphite calorimeter for use in high energy photons was

discussed. Comparison with ion chamber based dose

measurements showed good agreements

• A semi-empirical method was developed to simulate an

ion chamber for measurements of dose in the presence of

a magnetic field. Chamber measurements agreed well

with MC calculations

• Independent dosimetry audit for MRI linacs is being

developed by the Australian clinical dosimetry Service

Occupational dosimetry


• Presentation by ISO of all relevant standards for external

and internal individual monitoring of the staff, patient

dosimetry and related protocols in clinical applications and

for shielding systems

• Extremity dose monitoring

⎼ Correct measurements require a knowledge of the most

exposed area of the hand.

⎼ There is a need to have a clear strategy for extremity

dose monitoring

⎼ Syringe shields give significant dose reduction (80-90%,

UK results)



• Dosimetry to the lens of the eye:

⎼ reasonable estimate of the eye dose may be derived

from personal dosimeter (Hp(10)) data

⎼ The efficiency of different models of lead eye wear of

interventional clinicians has been assessed. The

potential to underestimate the dose to the eye lens was

highlighted



• Dosimetry of Accidental Exposure using Fingernails: It is a

major challenge to correct the individual-dependent changes

of the signal intensities when using the fingernail ESR

dosimetry method

• Assessment of Intakes of radionuclides for workers in

Nuclear medicine facilities: Although the occupational doses

are low there is a need to have a clear strategy for intakes

and dose assessment

Moving from measured to patient-specific

dose quantities


• The benefits of justified diagnostic radiology were

emphasized

• The challenges of the growing number of medical radiation

exposures as well as the growing complexity of the

diagnostic technology were outlined

• Confusion on the use of clinical dosimetric quantities/patient

dose indices still exists among some practitioners

(physicists, physicians, radiation safety specialists, etc)

Moving from measured to patient-specific

dose quantities


• The IAEA Code of Practice TRS 457 (2007) should be

updated to take into account new developments (modalities,

detectors, dose monitoring software, etc)

• It was emphasised that one should not use effective dose

calculations to extrapolate to future cancer risks as this was

totally inappropriate for diagnostic radiology

• Attention was drawn to the WHO leaflets and booklet on

communicating with parents and families of paediatric

patients

Thank you

IDOS-2019 Concluding session 39

idos 2019 symposium highlights · •trs 398 ⎼a plenary session describing the status of the...

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