Abstract

Purpose

To develop a Monte Carlo (MC) beam model for raster scanning proton beams for dose verification purposes.

Methods and materials

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.

Results

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.

Conclusions

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.

中文翻译：

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蒙特卡罗束模型的发展，用于光栅扫描质子束和剂量学比较。

摘要

目的

开发用于剂量扫描目的的光栅扫描质子束的蒙特卡洛（MC）束模型。

方法和材料

模型中使用了MC程序FLUKA。模型中的标称能量，动量散布和波束角分布是通过将模拟轮廓与测得的积分深度剂量（IDD）和空气斑大小相匹配来确定的。通过比较测得的剂量分布和模拟的剂量分布进行剂量学比较。立方扩散布拉格峰（SOBP）计划的一维剂量分布图和先前治疗过的乳腺癌患者的临床计划的二维剂量分布分别通过使用Pinpoint腔室和二维D型电离腔室进行测量。相应的DICOM计划信息用于MC仿真。

结果

MC结果显示与SOBP计划的测量结果吻合良好。MC与测量值之间的吸收剂量差的绝对比较为0.93％±0.88％。对于患者计划，以2％-2 mm的标准进行的MC模拟和测量之间的伽玛指数分析（γ-PR）的总通过率为97.78％，只有1例的γ-PR小于90％ 。使用3％-3 mm的标准，在有和没有档位移位器的情况下，γ-PR都不会低于99％。

结论

这项工作描述了一种适用于光栅扫描质子束的MC仿真模型的方法。仿真和测量之间的良好一致性表明，MC模型是一种准确而可靠的方法。它有可能用于特定患者的质量保证（PSQA），以减少在水中进行测量的光束时间。