This study aims to use TOPAS Monte Carlo (MC) code to model the beamline of a scanned proton therapy system in Shanghai Proton and Heavy Ion Center (SPHIC). This tool can be useful for treatment plan quality assurance. In-air lateral profiles of single proton spots at five positions along the Z-axis were measured, which can then be used to calculate the angular variance, spatial angular covariance, and spatial variance at the beam exit position. The mean energy and energy spread of the primary incident beam for 15 energies were tuned by comparing with measured relative integrated depth dose at the central axis. Three spread-out Bragg peak plans in homogeneous water cubes and one plan with a half anthropomorphic head phantom were created to verify the accuracy of the model. In addition, the comparison was also performed to RayStation TPS with an MC dose calculation engine for the plans. The average difference of spot sizes was 1.3% for all five energies. For all 15 energies, the average range (D90) difference was 0.04 mm, the mean distal-fall-off (DDF) difference was 0.04 mm, and the mean full width at half maximum (FWHM) difference was 0.10 mm. For the three homogeneous cube plans, a maximum difference of 0.2 mm for the D90 was observed, and the absolute differences in the lateral penumbras for each plan all agreed within 1 mm. For the plan on the anthropomorphic half head phantom, the mean dose deviation is less than 1.2% compared to measurements. We successfully developed an MC model for the proton scanning system used in SPHIC, which can be helpful for dose verification of the Treatment Planning System (TPS) and quality assurance in the future.

中文翻译：

---

SPHIC 扫描质子治疗系统的 TOPAS 蒙特卡罗模拟

本研究旨在使用 TOPAS 蒙特卡罗 (MC) 代码对上海质子重离子中心 (SPHIC) 扫描质子治疗系统的束线进行建模。该工具可用于保证治疗计划的质量。测量了沿 Z 轴五个位置的单个质子点的空气横向轮廓，然后可用于计算束流出口位置的角度方差、空间角协方差和空间方差。通过与中心轴处测得的相对积分深度剂量进行比较，调整了 15 种能量的主入射光束的平均能量和能量分布。创建了三个在均质水立方体中展开的布拉格峰计划和一个具有半拟人化头部模型的计划来验证模型的准确性。此外，还与带有 MC 剂量计算引擎的 RayStation TPS 进行了比较。所有五种能量的光斑尺寸平均差异为 1.3%。对于所有 15 种能量，平均射程 (D90) 差异为 0.04 毫米，平均远端衰减 (DDF) 差异为 0.04 毫米，平均半峰全宽 (FWHM) 差异为 0.10 毫米。对于三个均质立方体平面，观察到 D9​​0 的最大差异为 0.2 毫米，并且每个平面的横向半影的绝对差异均在 1 毫米以内。对于拟人半头模型的计划，与测量相比，平均剂量偏差小于 1.2%。我们成功开发了SPHIC质子扫描系统的MC模型，有助于未来治疗计划系统（TPS）的剂​​量验证和质量保证。