initial experiences in testing the iaea/aapm code of ... · 1. department of radiation oncology,...

Wolfgang Lechner1,2*, Mehenna Arib3, Paola Ballesteros-Zebadúa4, Karen Christaki5, Paolo Francescon6, Fernando Garcia-Yip7, M. Saiful Huq8, Anas Ismail9, Rajesh Kinhikar10, José Lárraga-Gutiérrez4, Karthick Raj Mani11,Debbie van der Merwe12, Otto Sauer13, Shaima Shoeir14, Sivalee Suriyapee15, Sonja Wegener13

Initial Experiences in Testing The IAEA/AAPM Code of Practice on Small Field Dosimetry

1 Department of Radiation Oncology, Division Medical Physics, Medical University Vienna, 1090 Vienna, Austria

2 Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University of Vienna, Austria

3 Biomedical Physics Department, King Faisal Specialist Hospital and Research Centre, Riyadh 11211,Kingdom of Saudi Arabia

4 Laboratorio de Física Médica, Instituto Nacional de Neurología y Neurocirugía, Mexico City, Mexico

5 International Atomic Energy Agency, Vienna International Centre, PO Box 100, 1400 Vienna, Austria

6 Medical Physics Department, Vicenza Hospital, Vicenza, Italy

7 Departamento de Radioterapia, Instituto Nacional de Oncologia y Radiobiologia, La Habana, Cuba

8 University of Pittsburgh cancer Institute and UPMC Cancer center, University of Pittsburgh, Pittsburgh, Pennsylvania, USA

9 Protection and Safety Department, Atomic Energy Commission of Syria, PO Box 6091, Damascus, Syria

10 Department of Medical Physics, Tata Memorial Centre, Mumbai, India 400015

11 Department of Radiation Oncology, United Hospital Ltd., Dhaka, Bangladesh

12 Department of Medical Physics, University of the Witwatersrand, Johannesburg, South Africa

13 Department of Radiation Oncology, University of Würzburg, 97080 Würzburg, Germany

14 Radiotherapy Department, Children's Cancer Hospital 57357 Kairo, Egypt

15 Division of Radiation Oncology, Department of Radiology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.

Affiliations

2 ICARO 2 / Small field dosimetry / Lechner 2017

http://www.meduniwien.ac.at/hp/radonc/

The financial support by the Federal Ministry of Science, Research and Economy and the National Foundation for Research, Technology and Development is gratefully acknowledged.

• Thanks to the team at Medical University of Vienna

‒ Dietmar Georg

‒ Gerd Heilemann

‒ Lukas Sölkner


• IAEA initiated a coordinated research project (CRP) on “Testing of

Code of Practice on small field dosimetry” (E2.40.21)

‒ Duration 2015 - 2018

‒ Objectives:

→ Testing the small field CoP

→ Assisting on implementation in clinical practice

→ Reduction of uncertainty in small field dosimetry

Motivation


• Step 1: testing the CoP in “standard” conditions

‒ C-arm Linac 6 MV WFF

→Simulation of determination of beam quality in msr-field

→Field output factor measurements down to 0.5 x 0.5 cm²

→Simulation of determination of absorbed dose to water in msr-

fields

→Simulation cross-calibration in msr-fields

→Determination of phantom-dose conversion factors

• Step 2: testing the CoP in “non-standard” conditions

‒ Same as step 1 but with FFF-beams, TomoTherapy,

CyberKnife and GammaKnife

Motivation


• Simulation of determination of beam quality in msr-field

‒ Determination of TPR20,10(10) or %dd(10,10)X using formalism

described in CoP

→ Experimental determination of TPR20,10(S) and/or %dd(10,S)X

o S = 4 x 4 cm² and 6 x 6 cm²

→ Comparison of calculated TPR20,10(10) or %dd(10,10)X to measured

TPR20,10 or %dd(10)X

• Determination field output factors according to the CoP

‒ Field sizes (cm²): 10 x 10, 6 x 6, 4 x 4, 3 x 3, 2 x 2, 1 x 1, 0.5 x 0.5

‒ Three different detectors

Materials and Methods


• Deviation of measured vs. calculated beam quality specifier less

than 1% for the majority of centers

Determination of beam quality - Results


• Available Detectors :

Relative dosimetry


Relative dosimetry Manuf. Detector #Centers PTW mircoDiamond 6

DiodeE 60012/17/18 4

DiodeP 60016 1 Diode 60008 1 PinPoint 31006 1 PinPoint 31016 3 Semiflex 1

IBA SFD 2 PFD 1 CC01 1

Sun Nuclear EDGE 2 Standard Imaging W1 1

Relative dosimetry Manuf. Linac Model # Centers

Elekta Versa HD 1 Synergy (Agility) 1 Synergy S 1

Σ 3

Varian TrueBEAM 2 TrueBEAM Stx 1 Varian21EX 1

Σ 4

Siemens Primus 2 Σ 2

• All measured field output factors, addition variation due to different

machines further assessment using standard error of field output factors

Relative dosimetry - results


frefclin

clin

frefclin

clin

frefclin

clin

fQQ

fQQ

fQQ kM ,

,,,

,, =Ω



• Standard error of ratio of readings

frefclin

clin

fQQM ,

,




• Can be improved by applying

correction factors

• Centers used only two detectors

and one of them was not suitable

for the field size

• Centers used more than two

detectors and one of them was

not suitable for the field size

frefclin

clin

frefclin

clin

frefclin

clin

fQQ

fQQ

fQQ kM ,

,,,

,, =Ω


• Can be improved by applying

correction factors

• Centers used only two detectors

and one of them was not suitable

for the field size

• Centers used more than two

detectors and one of them was

not suitable for the field size

• 3 results improved

• 1 deteriorated

• Centers were asked to repeat



frefclin

clin

frefclin

clin

frefclin

clin

fQQ

fQQ

fQQ kM ,

,,,

,, =Ω

• Determination of beam quality

‒ feasible within reasonable uncertainties

• Relative dosimetry

‒ Read the CoP thoroughly!

‒ Use at least two (better three) different detectors for small fields

‒ Do not use correction factors larger than 5%

→ Correction factors larger than 5% have been removed from the CoP

‒ Standard error of measured field output factors, using correction factors

published in the CoP, can be used as a tool for quality assurance for small

field dosimetry

→ If the standard error is too high repeat the measurement

• Beware the loss of lateral charged particle equilibrium

‒ E.g. Do not use a Farmer chamber in a 4 x 4 cm² field (example provided in CoP)

Recommendations / Lessons learned


initial experiences in testing the iaea/aapm code of ... · 1. department of radiation oncology,...

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