Prompt gamma detection during proton radiotherapy for range verification purposes will need to operate in both active and passive treatment beam environments. This paper describes prompt gamma measurements using a high resolution 2″ 2″ LaBr₃ detector for a 200 MeV clinical passive-scatter proton beam. These measurements examine the most likely discrete prompt gamma rays emitted from tissue by detecting gammas produced in water, Perspex, carbon and liquid-nitrogen targets. Measurements were carried out at several positions around the depth corresponding to the location of the Bragg peak for water and Perspex targets in order to investigate prompt gamma emission as a function of depth along the beam path. This work also focused on validating the Geant4 Monte Carlo model of the passive-scatter proton beam line and LaBr₃ detector by making a direct comparison between the simulated and experimental results. The initial prompt gamma measurements were overwhelmed by the high amount of scattered radiation when measuring at isocenter, shifting the target further downstream from the final collimator significantly reduced the background radiation. Prompt gamma peaks were then clearly identified for the water, Perspex and graphite targets. The developed Geant4 Monte Carlo model was able to replicate the measured prompt gamma ray energy spectra, including production for important photopeaks to within 10%, except for the 4.44 MeV peak from the water target, which had more than a 50% overestimation of the number of produced prompt gamma rays. The prompt gamma measurements at various depths correlated well with the proton dose deposition; the 4.44 and 6.13 MeV photopeak profiles peaked within 1 cm of the Bragg peak and the R_50% value for the 3–7 MeV energy range predicted the proton range within 8 mm.

质子放射治疗期间用于范围验证的即时伽马检测需要在主动和被动治疗束环境中运行。本文介绍了使用高分辨率 2" 2" LaBr _{3 进行}快速伽马测量200 MeV 临床被动散射质子束检测器。这些测量通过检测在水、有机玻璃、碳和液氮目标中产生的伽马射线来检查最有可能从组织发出的离散瞬发伽马射线。在与水和有机玻璃目标的布拉格峰位置相对应的深度周围的几个位置处进行测量，以研究作为沿光束路径深度的函数的即时伽马发射。这项工作还侧重于验证被动散射质子束线和 LaBr ₃的 Geant4 Monte Carlo 模型通过在模拟和实验结果之间进行直接比较。在等中心进行测量时，最初的即时伽马测量被大量散射辐射淹没，将目标移到最终准直器的更下游，显着降低了背景辐射。然后清楚地识别出水、有机玻璃和石墨目标的快速伽马峰。开发的 Geant4 Monte Carlo 模型能够复制测量的瞬发伽马射线能谱，包括产生 10% 以内的重要光峰，除了来自水目标的 4.44 MeV 峰，其高估了 50% 以上的数量产生的瞬发伽马射线。不同深度的即时伽马测量与质子剂量沉积有很好的相关性；4.44 和 6。3-7 MeV 能量范围的_50%值预测了 8 mm 内的质子范围。