YAO Xing-hong,CHEN Li-xin,JIN Guang-hua.Comparative determination of absorbed doses for high-energy photon beam with different cylindrical chambers[J].Chinese Journal of Radiological Medicine and Protection,2012,32(4):412-415
Comparative determination of absorbed doses for high-energy photon beam with different cylindrical chambers
Received:October 21, 2011  
DOI：10.3760/cma.j.issn.0254-5098.2012.04.023
KeyWords:Cylindrical chambers  Photon beam  Absorbed dose  TRS-277  TRS-398
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Author NameAffiliationE-mail
YAO Xing-hong State Key Laboratory of Oncology in South China, Department of Radiation Oncology, Sun Yat-Sen University Cancer Center, Guangzhou 510060, China  
CHEN Li-xin State Key Laboratory of Oncology in South China, Department of Radiation Oncology, Sun Yat-Sen University Cancer Center, Guangzhou 510060, China chenlx@sysucc.org.cn 
JIN Guang-hua 中山大学物理科学与技术工程学院  
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Abstract::
      Objective To study the difference between the IAEA code of practice TRS-277 and TRS-398 in the determination of the absorbed dose to water for high-energy photon beams using several cylindrical chambers.Methods For 6 different types of cylindrical chambers, the calibration factors ND,w,Q0 in terms of absorbed dose to water were calculated from the air exposure calibration factors Nx, and were compared with the ND,w,Q0 measured in European standard laboratory. Accurate measurements were performed in Varian 6 MV photon beam using 6 cylindrical chambers according to TRS-277 and TRS-398. The beam quality correction factors kQ,Q0 as well as the water absorbed doses were compared. Results For the set of chambers, the difference between ND,w,Q0 computed from Nx and ND,w,Q0 obtained in European standard laboratory was 0.13%~1.30%. The difference of beam quality correction factors for TRS-277 and TRS-398 was 0.09%~0.45%. The distinction of the water absorbed doses obtained according to the two different protocols was 0.27%~1.40%, and was primarily due to their different calibration factors. Conclusions The discrepancy in absorbed doses determined according to two protocols using different cylindrical chambers is clinically acceptable. However, TRS-398 allows a more convenient localization of chambers, provides a more simple formulation, and offers the reduced uncertainty in the dosimetry of radiotherapy beams.
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