Prateepkaew Jakkrit, Matsubayashi Nishiki, Takata Takushi, Tanaka Hiroki, Sakurai Yoshinori
Graduate School of Engineering, Kyoto University, Kyoto Daigaku-katsura, Nishikyo-ku, Kyoto, Japan.
Institute for Integrated Radiation and Nuclear Science, Kyoto University, Sennan-gun, Osaka, Japan.
Med Phys. 2025 Aug;52(8):e18029. doi: 10.1002/mp.18029.
The neutron beam in a boron neutron capture therapy (BNCT) irradiation field comprises a range of energies with different relative biological effectiveness. The neutron energy spectrum can change over time due to variations in the neutron source. Current methods for measuring the neutron energy spectrum are impractical and have significant limitations, such as being time-consuming and posing radiation exposure risks; therefore, neutron energy spectrum measurement has not been incorporated into routine BNCT quality assurance (QA) procedures. To address these issues, we developed a cylindrical hemisphere accurate remote multilayer spectrometer (CHARMS) that integrates a liquid moderator supply and drainage system with real-time neutron detection for suitable use in the BNCT QA procedure.
To validate CHARMS for QA procedures in BNCT irradiation field.
We conducted experimental validations of CHARMS at the Heavy Water Neutron Irradiation Facility of Kyoto University Reactor under two irradiation conditions (with and without a collimator), performing three separate measurement sessions over 3 months.
The total measurement time required by CHARMS to achieve a target neutron count uncertainty below 1% was less than 10 min. Monitoring the neutron counts at ten uniformly spaced intervals during each measurement showed that most counts fell within a Poisson-derived standard deviation. The neutron energy spectrum under irradiation without collimator was successfully evaluated. However, because of the effects of the neutron beam intensity and angular distribution in BNCT, the neutron energy spectrum under irradiation with collimator could not be properly evaluated.
The validity of the CHARMS for QA procedures in BNCT was confirmed. The rapid measurements and stable operation of the liquid moderator injection and drainage system show that CHARMS is well-suited for routine BNCT QA, eliminating the need for moderator replacement and thereby minimizing radiation exposure. Future work will address the challenges related to neutron beam intensity and angular distribution to enable the evaluation of neutron energy spectrum unfolding under collimated irradiation conditions, which is essential for clinical BNCT.
硼中子俘获疗法（BNCT）辐照场中的中子束包含一系列具有不同相对生物效应的能量。由于中子源的变化，中子能谱会随时间变化。当前测量中子能谱的方法不切实际且有显著局限性，比如耗时且存在辐射暴露风险；因此，中子能谱测量尚未纳入常规BNCT质量保证（QA）程序。为解决这些问题，我们开发了一种圆柱形半球精确远程多层光谱仪（CHARMS），它集成了液体慢化剂供应和排水系统以及实时中子探测功能，适用于BNCT QA程序。
验证CHARMS在BNCT辐照场QA程序中的有效性。
我们在京都大学反应堆重水中子辐照设施下，在两种辐照条件（有准直器和无准直器）下对CHARMS进行了实验验证，在3个月内进行了三次单独的测量。
CHARMS实现目标中子计数不确定度低于1%所需的总测量时间少于10分钟。在每次测量期间以十个均匀间隔监测中子计数表明，大多数计数落在泊松推导的标准偏差范围内。成功评估了无准直器辐照下的中子能谱。然而，由于BNCT中中子束强度和角分布的影响，有准直器辐照下的中子能谱无法得到正确评估。
证实了CHARMS在BNCT QA程序中的有效性。液体慢化剂注入和排水系统的快速测量和稳定运行表明，CHARMS非常适合常规BNCT QA，无需更换慢化剂，从而将辐射暴露降至最低。未来的工作将解决与中子束强度和角分布相关的挑战，以便能够评估准直辐照条件下的中子能谱展开，这对临床BNCT至关重要。
