Monte Carlo simulations using the Geant4 toolkit are widely used in proton therapy to predict the dose distribution and secondary particle production. The choice of physics models used in the simulation can greatly affect the accuracy of the results. However, general hadronic models in Geant4 are not specifically tuned for medical physics regions and available experimental data are still limited. In this study, we investigated three different Geant4 hadronic physics models: BIC, BERT, and INCL++, by calculating the yields and kinematical distribution of the secondary neutron, gamma, and positron emitters as well as their incident energy dependence. The simulations were performed for a water phantom irradiated with 70 – 250 MeV proton beams. Our analysis revealed significant differences in the yields, angular, and energy distributions of emitted secondary particles between the three models. We also found a systematic underestimation of yields for the positron emitter 11C in the recent version 10.7 of Geant4. Overall, our study highlights the importance of carefully selecting a hadronic physics model for Geant4 simulations in proton therapy. Our findings also emphasize the need for a specifically tuned Geant4 hadronic model for proton therapy applications in order to consistently reproduce a wide range of important observables. More experimental data for proton-induced reactions in human tissue are critically needed to constrain and validate the suitable physics models for proton therapy simulation.

中文翻译：

---

Geant4 强子物理模型对质子治疗模拟中二次粒子产生的影响


使用 Geant4 工具包的蒙特卡罗模拟广泛用于质子治疗，以预测剂量分布和二次颗粒的产生。仿真中使用的物理模型的选择会极大地影响结果的准确性。然而，Geant4 中的通用强子模型并未专门针对医学物理区域进行调整，并且可用的实验数据仍然有限。在这项研究中，我们通过计算次级中子、γ 和正电子发射器的产量和运动学分布以及它们的入射能量依赖性，研究了三种不同的 Geant4 强子物理模型：BIC、BERT 和 INCL++。对用 70 – 250 MeV 质子束照射的水体模进行了模拟。我们的分析揭示了三种模型之间发射的二次粒子的产率、角度和能量分布存在显著差异。我们还发现，在最近的 Geant4 10.7 版本中，系统性地低估了正电子发射器 11C 的产率。总体而言，我们的研究强调了在质子治疗中为 Geant4 模拟仔细选择强子物理模型的重要性。我们的研究结果还强调了质子治疗应用需要专门调整的 Geant4 强子模型，以便始终如一地再现各种重要的可观察对象。迫切需要更多关于人体组织中质子诱导反应的实验数据，以约束和验证适合质子治疗模拟的物理模型。