Department of Medical Physics, Shanghai Proton and Heavy Ion Center, Shanghai, China.
Shanghai Engineering Research Center of Proton and Heavy Ion Radiation Therapy, Shanghai, China.
Int J Radiat Biol. 2020 Nov;96(11):1435-1442. doi: 10.1080/09553002.2020.1812758. Epub 2020 Sep 2.
To develop a Monte Carlo (MC) beam model for raster scanning proton beams for dose verification purposes.
MC program FLUKA was used in the model. The nominal energy, momentum spread and beam angular distribution in the model were determined by matching the simulation profiles with the measured integral depth dose (IDD) and in air spot size. Dosimetric comparison was done by comparing the measured and simulated dose distributions. The 1 D dose profile of cubic Spread Out Bragg Peak (SOBP) plans, and the 2 D dose distribution of previously treated breast cancer patients' clinical plans were measured by using Pinpoint chambers and 2 D array ionization chambers, respectively. Corresponding DICOM plan information was utilized for MC simulation.
The MC results showed good agreement with measurements for the SOBP plans. The absolute comparison of the absorbed dose difference between the MC and the measurement was 0.93%±0.88%. For the patient plans, the overall passing rate of the gamma index analysis (γ-PR) between the MC simulation and measurement with the 2%-2 mm criteria was 97.78%, and only 1 case had a γ-PR less than 90%. With the 3%-3 mm criteria, γ-PR was never below 99% for all cases with and without the range shifter.
This work described a method for adapting a MC simulation model for a raster scanning proton beam. The good concordance between the simulations and measurements shows that the MC model is an accurate and reliable method. It has the potential to be used for patient specific quality assurance (PSQA) to reduce the beam time for the measurements in water.
开发用于剂量验证的扫描质子束蒙特卡罗（MC）束模型。
在模型中使用 MC 程序 FLUKA。通过将模拟轮廓与测量的积分深度剂量（IDD）和空气中的光斑大小相匹配，确定模型中的标称能量、动量分布和束角分布。通过比较测量和模拟的剂量分布来进行剂量比较。使用 Pinpoint 室和二维电离室分别测量立方扩展布拉格峰（SOBP）计划的一维剂量分布和先前治疗的乳腺癌患者临床计划的二维剂量分布。相应的 DICOM 计划信息用于 MC 模拟。
MC 结果与 SOBP 计划的测量结果吻合良好。MC 和测量之间吸收剂量差异的绝对比较为 0.93%±0.88%。对于患者计划，在 2%-2mm 标准下，MC 模拟与测量之间的伽马指数分析（γ-PR）的总体通过率为 97.78%，只有 1 例γ-PR 低于 90%。在 3%-3mm 标准下，所有有和没有射程移动器的情况下，γ-PR 从未低于 99%。
这项工作描述了一种适用于扫描质子束的 MC 模拟模型的方法。模拟与测量之间的良好一致性表明，MC 模型是一种准确可靠的方法。它有可能用于患者特定的质量保证（PSQA），以减少在水中进行测量的束时间。
