A Comparative Study of Reference Dosimetries in Japan and Canada
A Comparative Study of Reference Dosimetries in Japan and Canada
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日本和加拿大参考剂量测定的比较研究
DOI：
10.11323/jjmp.37.1_25
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
齋藤 秀敏
中科院分区：
文献类型：
--
作者：
河内 徹;片寄 哲朗;兒玉 匠;宮阪 遼平;清水 森人;齋藤 秀敏
在日本和北美，已经实施了不同的剂量测定方案来确定水的吸收剂量：JSMP标准剂量测定12和AAPM TG-51附录。本文对日本和加拿大的高能光子束参考剂量学进行了理论比较，并进行了实验验证。估算了离子复合修正因子、泄漏修正因子、径向剂量分布修正因子、校准因子、束流质量修正因子和水吸收剂量的理论差异。当径向剂量分布的影响可以忽略不计时，加拿大对日本的吸收剂量比在参考剂量测定中的范围为0.995至1.007，对于所有的参考级-农民型电离室。这种差异主要是由光束质量校正因子中包含的壁校正因子引起的。随后，为了验证理论方法，我们在日本初级和次级标准剂量学实验室（PSDL和SSDL）的60 Co γ射线中校准了相同的电离室，并测量了临床直线加速器的吸收剂量。因此，对于PTW 30013参考级农民型电离室，参考剂量测定中加拿大与日本吸收剂量的比值增加到1.015。这种增加主要是由日本PSDL和SSDL之间观察到的校准因子（N D，w）的差异造成的。总之，为了提高JSMP标准剂量学12测定的水吸收剂量的国际一致性，应重新评价壁校正因子的准确性，并对日本PSDL和SSDL之间的N D，w进行定期比较试验。
In Japan and North America, different dosimetry protocols have been implemented to determine the absorbed dose to water: JSMP Standard Dosimetry 12 and AAPM TG-51 addendum. In this study, Japanese and Canadian reference dosimetries for high energy photon beams were compared theoretically, and then they were verified experimentally. We estimated the theoretical differences of the ion recombination correction factors, the leakage correction factors, the radial dose distribution correction factors, the calibration factors, the beam quality correction factors and the absorbed dose to water. When an influence of the radial dose distribution is negligible, the ratios of Canadian to Japanese absorbed dose in reference dosimetries ranged from 0.995 to 1.007 for all the reference-class-Farmer-type ionization chambers. This discrepancy was mainly caused by the wall correction factor included in the beam quality correction factor. Subsequently, to verify the theoretical approaches, we calibrated the same ionization chamber in 60 Co gamma ray of Japanese primary and secondary standard dosimetry laboratories (PSDL and SSDL) and measured the absorbed dose of a clinical linear accelerator. It followed that the ratios of Canadian to Japanese absorbed dose in reference dosimetries increased up to 1.015 for PTW 30013 reference-class-Farmer-type ionization chamber. This increase was mainly caused by a discrepancy in the calibration factors (N D, w) observed between Japanese PSDL and SSDL. In conclusion, in order to improve the international consistency of the absorbed dose to water determined by JSMP Standard Dosimetry 12, we should reevaluate the accuracy of the wall correction factors and implement a periodic comparative test of the N D, w between Japanese PSDL and SSDL.