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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
3 ICARO 2 / Small field dosimetry / Lechner 2017
• 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
4 ICARO 2 / Small field dosimetry / Lechner 2017
• 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
5 ICARO 2 / Small field dosimetry / Lechner 2017
• 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
6 ICARO 2 / Small field dosimetry / Lechner 2017
• Deviation of measured vs. calculated beam quality specifier less
than 1% for the majority of centers
Determination of beam quality - Results
7 ICARO 2 / Small field dosimetry / Lechner 2017
• Available Detectors :
Relative dosimetry
8 ICARO 2 / Small field dosimetry / Lechner 2017
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
9 ICARO 2 / Small field dosimetry / Lechner 2017
frefclin
clin
frefclin
clin
frefclin
clin
fQQ
fQQ
fQQ kM ,
,,,
,, =Ω
Relative dosimetry - results
10 ICARO 2 / Small field dosimetry / Lechner 2017
• Standard error of ratio of readings
frefclin
clin
fQQM ,
,
Relative dosimetry - results
11 ICARO 2 / Small field dosimetry / Lechner 2017
• Standard error of ratio of readings
• 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
• Standard error of ratio of readings
• 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
Relative dosimetry - results
12 ICARO 2 / Small field dosimetry / Lechner 2017
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
13 ICARO 2 / Small field dosimetry / Lechner 2017