Indiana University Cyclotron Operations, Bloomington, IN 47405, USA.
Phys Med Biol. 2010 Dec 21;55(24):7509-22. doi: 10.1088/0031-9155/55/24/008. Epub 2010 Nov 19.
Proton beam losses in various components of a treatment nozzle generate secondary neutrons, which bring unwanted out of field dose during treatments. The purpose of this study was to develop an analytic method for estimating neutron dose to a distant organ at risk during proton therapy. Based on radiation shielding calculation methods proposed by Sullivan, we developed an analytical model for converting the proton beam losses in the nozzle components and in the treatment volume into the secondary neutron dose at a point of interest. Using the MCNPx Monte Carlo code, we benchmarked the neutron dose rates generated by the proton beam stopped at various media. The Monte Carlo calculations confirmed the validity of the analytical model for simple beam stop geometry. The analytical model was then applied to neutron dose equivalent measurements performed on double scattering and uniform scanning nozzles at the Midwest Proton Radiotherapy Institute (MPRI). Good agreement was obtained between the model predictions and the data measured at MPRI. This work provides a method for estimating analytically the neutron dose equivalent to a distant organ at risk. This method can be used as a tool for optimizing dose delivery techniques in proton therapy.
在治疗喷嘴的各种组件中，质子束损失会产生次级中子，在治疗过程中会带来不必要的场外剂量。本研究的目的是开发一种分析方法，用于估算质子治疗期间远处危险器官的中子剂量。基于沙利文（Sullivan）提出的辐射屏蔽计算方法，我们开发了一种分析模型，可将喷嘴组件和治疗体积中的质子束损失转换为感兴趣点的次级中子剂量。我们使用 MCNPx 蒙特卡罗代码对在各种介质中停止的质子束产生的中子剂量率进行了基准测试。蒙特卡罗计算证实了该分析模型对于简单束停止几何形状的有效性。然后，将该分析模型应用于在中西部质子放射治疗研究所（MPRI）进行的双散射和均匀扫描喷嘴的中子剂量当量测量。模型预测与 MPRI 测量的数据之间得到了很好的一致性。这项工作提供了一种分析估算远处危险器官中子剂量当量的方法。该方法可用作优化质子治疗中剂量输送技术的工具。
