SU-E-T-499：瓦里安通用相空间文件用于TrueBeam直线加速器机头剂量分布蒙特卡罗计算的验证

SU-E-T-499: Validation of the Varian Generic Phase Space Files for Monte Carlo Calculations of Dose Distributions for the TrueBeam Linac Head.

作者信息

Wang L, Xing L, Sawkey D, Constantin M, Svatos M, Mok E

机构信息

Stanford University School of Medicine, Stanford, CA.

Varian Medical Systems, Palo Alto, CA.

出版信息

Med Phys. 2012 Jun;39(6Part17):3820. doi: 10.1118/1.4735588.

DOI:10.1118/1.4735588

PMID:28517461

Abstract

PURPOSE

To validate the generic phase space files for Varian TrueBeam linac head simulations.

METHODS

The generic phase space files include the simulation results of 6MV, 10MV, 6MV FFF, and 10MV FFF (flattening-filter free) operating modes of TrueBeam for patient-independent linac head components. Using the generic phase space files as the radiation sources, the BEAMnrc Monte Carlo codes are used to simulate the patient-dependent parts of the TrueBeam linac and the resulting phase space files are generated at a plane just before entering a water phantom for 4 different field sizes (5×5, 10×10, 20×20, and 40×40 cm ). Dose distributions are calculated by DOSXYZnrc in the water phantom of size 50×50×40 cm . The percentage-depth-dose (PDD) curves and lateral dose profiles at three different depths (dmax, 10cm, 20cm) are obtained. Comprehensive comparisons have been made for a total of 64 dose profiles (including PDDs) between the Monte Carlo calculations and the measured data. The gamma index analysis is performed for all the comparisons.

RESULTS

The matching of the calculated dose distributions to the measured ones is analyzed by the gamma index method with a criterion of 2% dose tolerance and 2 mm distance-to-agreement. Of the 64 comparisons, the minimum gamma index passing rate is at least 92%, after taking into account the statistical nature of the Monte Carlo calculated dose values. Despite the existence of latent variance of phase space files, the phantom dose calculation uncertainty can be less than 1% for field sizes as small as 5×5 cm . The computing time saved by using phase space files could be a factor of 5-10.

CONCLUSIONS

The Varian generic phase space files are accurate and efficient radiation sources for Monte Carlo calculations of radiation dose distributions for TrueBeam linac head. This work was supported in part by Varian Medical Systems and the NIH (1R01 CA104205 and 1R21 CA153587).

摘要

目的

验证瓦里安TrueBeam直线加速器机头模拟的通用相空间文件。

方法

通用相空间文件包含TrueBeam的6MV、10MV、6MV FFF和10MV FFF（无均整器）运行模式下与患者无关的直线加速器机头组件的模拟结果。以通用相空间文件作为辐射源，使用BEAMnrc蒙特卡罗代码模拟TrueBeam直线加速器中与患者有关的部分，并在即将进入水模体之前的平面上针对4种不同射野尺寸（5×5、10×10、20×20和40×40 cm）生成所得的相空间文件。通过DOSXYZnrc在尺寸为50×50×40 cm的水模体中计算剂量分布。获得了三个不同深度（最大剂量深度、10 cm、20 cm）处的百分深度剂量（PDD）曲线和侧向剂量分布。对蒙特卡罗计算结果与测量数据之间总共64个剂量分布（包括PDD）进行了全面比较。对所有比较进行了伽马指数分析。

结果

采用剂量容差为2%、距离一致性为2 mm的标准，通过伽马指数法分析计算得到的剂量分布与测量剂量分布的匹配情况。在64次比较中，考虑到蒙特卡罗计算剂量值的统计特性，最小伽马指数通过率至少为92%。尽管相空间文件存在潜在差异，但对于小至5×5 cm的射野尺寸，模体剂量计算不确定度可小于1%。使用相空间文件节省的计算时间可能为5到10倍。