TOPAS 蒙特卡罗模拟在双散射质子治疗中的应用及剂量学评估。

TOPAS Monte Carlo simulation for double scattering proton therapy and dosimetric evaluation.

机构信息

Department of Physics, University of Science and Technology of China, Hefei, Anhui, China; University of Florida Health Proton Therapy Institute, Jacksonville, FL, USA.

University of Florida Health Proton Therapy Institute, Jacksonville, FL, USA.

出版信息

Phys Med. 2019 Jun;62:53-62. doi: 10.1016/j.ejmp.2019.05.001. Epub 2019 May 9.

DOI:10.1016/j.ejmp.2019.05.001

PMID:31153399

Abstract

PURPOSE

To construct and commission a double scattering (DS) proton beam model in TOPAS Monte Carlo (MC) code. Dose comparisons of MC calculations to the measured and treatment planning system (TPS) calculated dose were performed.

METHODS

The TOPAS nozzle model was based on the manufacturer blueprints. Nozzle set-up and beam current modulations were calculated using room-specific calibration data. This model was implemented to reproduce pristine peaks, spread-out Bragg peaks (SOBP) and lateral profiles. A stair-shaped target plan in water phantom was calculated and compared to measured data to verify range compensator (RC) modeling.

RESULTS

TOPAS calculated pristine peaks agreed well with measurements, with accuracies of 0.03 cm for range R and 0.05 cm for distal dose fall-off (DDF). The calculated SOBP range, modulation width and DDF differences between MC calculations and measurements were within 0.05 cm, 0.5 cm and 0.03 cm respectively. MC calculated lateral penumbra agreed well with measured data, with difference less than 0.05 cm. For RC calculation, TPS underestimated the additional depth dose tail due to the nuclear halo effect. Lateral doses by TPS were 10% lower than measurement outside the target, while maximum difference of MC calculation was within 2%. At deeper depths inside the target volume, TPS overestimated doses by up to 25% while TOPAS predicted the dose to within 5% of measurements.

CONCLUSION

We have successfully developed and commissioned a MC based DS nozzle model. The performance of dose accuracy by TOPAS was superior to TPS, especially for highly inhomogeneous compensator.

摘要

目的

在 TOPAS 蒙特卡罗（MC）代码中构建和调试双散射（DS）质子束模型。将 MC 计算的剂量与测量值和治疗计划系统（TPS）计算的剂量进行比较。

方法

TOPAS 喷嘴模型基于制造商的蓝图。使用特定房间的校准数据计算喷嘴设置和束流调制。该模型旨在重现原始峰、扩展布拉格峰（SOBP）和横向轮廓。在水模中计算了阶梯状靶区计划，并与测量数据进行比较，以验证剂量补偿器（RC）建模。

结果

TOPAS 计算的原始峰与测量值吻合良好，射程 R 的精度为 0.03 cm，远端剂量下降（DDF）的精度为 0.05 cm。MC 计算的 SOBP 射程、调制宽度和 DDF 与测量值的差异分别在 0.05 cm、0.5 cm 和 0.03 cm 以内。MC 计算的横向半影与测量数据吻合良好，差异小于 0.05 cm。对于 RC 计算，TPS 由于核晕效应低估了附加深度剂量尾部。TPS 外侧靶区的横向剂量比测量值低 10%，而 MC 计算的最大差异在 2%以内。在靶区内部更深的深度，TPS 高估剂量高达 25%，而 TOPAS 预测的剂量与测量值相差 5%以内。