重离子束水吸收剂量的电离法实验研究

Experimental Study for Absorbed-dose to Water of Heavy Ion Beam via Ionization Method

重离子束水吸收剂量是开展重离子束治疗最基本的物理量。在开展重离子束水吸收剂量的量值复现研究前,需用间接测量的方法开展相关工作以熟悉实验条件。本文用传统电离法开展了能量400 MeV/u、具有6 cm展宽Bragg峰的碳离子束的水吸收剂量测量研究,并评价了重离子束条件下的相关电离室的极化、离子复合修正因子。在电离室的极化和离子复合修正项方面,重离子束水吸收剂量测量的相关不确定度分量显著大于^60Coγ辐射水吸收剂量的相关值。用不同电离室测量重离子束水吸收剂量的结果在不确定度允许的范围内符合。以电离室测量为基础,开展更深入的包括量热法绝对测量在内的辐射剂量学研究,对进一步优化重离子束水吸收剂量测量的不确定度至关重要。

The absorbed-dose to water of heavy ion beam is a fundamental quantity for heavy ion therapy.It is necessary to perform the relevant work with in-direct measurement prior to the study of the reproduction for the absorbed-dose to water of heavy ion beam.The absorbed-dose to water of a carbon ion beam,whose incident energy was 400 MeV/u and spread-out Bragg peak was 6 cm,was studied with conventional ionization method.The correction factors of polarity and ion recombination for the ionization chambers were evaluated with the incident heavy ion beam.The uncertainty components for the measurement of the absorbed-dose to water of heavy ion beam are significantly larger than that of the ^60Coγradiation,in terms of the corrections for the polarity and ion recombination of the ionization chambers.The absorbed-dose to water of heavy ion beam deduced from different ionization chambers is consistent within the acceptance of uncertainty.Based on the measurement with ionization chambers,it is crucial to conduct more intensive research activities of radiation dosimetry including the absolute measurement with calorimetric facility,with the purpose of further optimizing the uncertainty in the measurement for the absorbed-dose to water of heavy ion beam.