Osaka Medical and Pharmaceutical University, Kansai BNCT Medical Center, Osaka, Japan.
Institute for Integrated Radiation and Nuclear Science, Kyoto University, Osaka, Japan.
J Appl Clin Med Phys. 2024 Nov;25(11):e14493. doi: 10.1002/acm2.14493. Epub 2024 Aug 27.
Neutron beams utilized for performing BNCT are composed of a mixture of neutrons and gamma rays. Although much of the dose delivered to the cancer cells comes from the high LET particles produced by the boron neutron capture reaction, the dose delivered to the healthy tissues from unwanted gamma rays cannot be ignored. With the increase in the number of accelerators for BNCT, a detector system that is capable of measuring gamma ray dose in a mixed neutron/gamma irradiation field is crucial. Currently, BeO TLDs encased in quartz glass are used to measure gamma ray dose in a BNCT irradiation field. However, this type of TLD is no longer commercially available. A replacement dosimetry system is required to perform the recommended ongoing quality assurance of gamma ray measurement for a clinical BNCT system.
The purpose of this study is to evaluate the characteristics of a BeO OSLD detector system under a mixed neutron and gamma ray irradiation field and to assess the suitability of the system for routine quality assurance measurements of an accelerator-based BNCT facility.
The myOSLD system by RadPro International GmbH was evaluated using the accelerator-based neutron source designed for clinical BNCT (NeuCure BNCT system). The readout constancy, linearity, dose rate effect, and fading effect of the OSLD were evaluated. Free-in-air and water phantom measurements were performed and compared with the TLD results and Monte Carlo simulation results. The PHITS Monte Carlo code was used for this study.
The readout constancy was found to be stable over a month-long period and similar to the TLD results. The OSLD readout signal was found to be linear, with a high coefficient of determination (R ≥ 0.999) up to a proton charge of 3.6 C. There was no significant signal fading or dose rate dependency. The central axis depth dose and off-axis dose profile measurements agreed with both the TLD and Monte Carlo simulation results, within one standard deviation.
The myOSLD system was characterized using an accelerator system designed for clinical BNCT. The experimental measurements confirmed the OSLD achieved similar, if not superior to, the currently utilized dosimetry system for routine QA of an accelerator-based BNCT system. The OSLD system would be a suitable replacement for the current TLD system for performing routine QA of gamma ray dose measurement in a BNCT irradiation field.
用于执行硼中子俘获治疗（BNCT）的中子束由中子和伽马射线的混合物组成。尽管硼中子俘获反应产生的高传能线密度（LET）粒子为癌细胞提供了大部分剂量，但来自无用伽马射线的健康组织剂量也不容忽视。随着 BNCT 加速器数量的增加，能够在混合中子/伽马辐照场中测量伽马射线剂量的探测器系统至关重要。目前，在 BNCT 辐照场中测量伽马射线剂量时，使用的是封装在石英玻璃中的 BeO 热释光剂量计（TLD）。然而，这种类型的 TLD 已不再商业供应。需要一种替代剂量测量系统来对临床 BNCT 系统的伽马射线测量进行推荐的常规质量保证。
本研究的目的是评估混合中子和伽马射线辐照场中 BeO 光释光探测器系统的特性，并评估该系统用于基于加速器的 BNCT 设施常规质量保证测量的适用性。
使用专为临床 BNCT 设计的基于加速器的中子源（NeuCure BNCT 系统）对 RadPro International GmbH 的 myOSLD 系统进行了评估。评估了光释光探测器的读出稳定性、线性度、剂量率效应和退光效应。进行了自由空气和水模体测量，并将结果与 TLD 结果和蒙特卡罗模拟结果进行了比较。本研究使用了 PHITS 蒙特卡罗代码。
在长达一个月的时间内，读出稳定性被发现是稳定的，与 TLD 结果相似。光释光探测器的读出信号是线性的，在质子电荷量为 3.6 C 时，决定系数（R≥0.999）很高。没有明显的信号退光或剂量率依赖性。中央轴深度剂量和离轴剂量分布测量结果与 TLD 和蒙特卡罗模拟结果一致，在一个标准差范围内。
使用专为临床 BNCT 设计的加速器系统对 myOSLD 系统进行了特征描述。实验测量结果证实，光释光探测器的性能与目前用于基于加速器的 BNCT 系统常规质量保证的剂量计系统相似，如果不是更好的话。光释光探测器系统将是替代目前用于 BNCT 辐照场中伽马射线剂量测量常规质量保证的 TLD 系统的合适选择。
