TrueBeam加速器6 MV非均整模式X射线的蒙特卡罗模拟

目的 对TrueBeam加速器6 MV非均整模式(FFF)X射线蒙特卡罗模拟,寻找最佳的模型参数,为进一步研究6 MV FFF X射线临床剂量学奠定模型基础。方法 借助BEAMnrc和DOSXYZnrc程序,调整入射电子束能量、径向强度分布及角度展宽等参数,对TrueBeam加速器6 MV FFF X射线4 cm×4 cm到40 cm×40 cm射野的百分深度剂量(PDD)和离轴比(OAR)曲线进行蒙特卡罗模拟,比较不同大小射野情况下模拟和测量结果的差异。结果 在入射电子能量为6.1 MeV、半高宽(FWHM)为0.75 mm和角度展宽为0.9°时,模拟结果与相应条件下实际测量结果最接近。不同射野的PDD和30 cm×30 cm及以下射野的OAR曲线与测量数据相比满足Local Dose的限制条件,剂量误差< 1%,位置误差< 1 mm;40 cm×40 cm射野的OAR满足剂量误差<1.5%,位置误差<1 mm的限制条件。结论 本模型模拟结果与实际测量结果一致性较好,可将模型参数用于6 MV FFF X射线临床剂量学研究。

Monte Carlo simulation of 6 MV flattening-filter-free beams in TrueBeam accelerator

Objective To find the best model parameters through Monte Carlo simulation of 6 MV flattening-filter-free (FFF) beams in TrueBeam accelerator, and establish the foundation for the further study of the clinical dosimetry on 6 MV FFF X-rays. Methods Using the BEAMnrc and DOSXYZnrc codes, the percentage depth dose (PDD) and the off-axis ratio (OAR) curves of field ranges from 4 cm×4 cm to 40 cm×40 cm were simulated for 6 MV FFF X-ray by adjusting the incident beam energy, radial intensity distribution and angular spread, respectively. The simulation results and measured data were compared, where the optimal Monte Carlo model input parameters were acquired. Results The simulation was most comparable to the measurement when the incident electron energy, full width at half maximum (FWHM) and the spread angle were set as 6.1 MeV, 0.75 mm and 0.9°, respectively. The deviation of 1 mm (position)/1% (local dose) could be met by the PDD of all tested field sizes and by the OAR when the fields sizes were no larger than 30 cm ×30 cm. The OAR of 40 cm×40 cm field sizes fulfilled criteria of 1 mm (position)/1.5% (local dose). Conclusions Monte Carlo simulation agrees well with the measurement and the proposed model parameters, which can be used for further clinical dosimetry studies of 6 MV FFF X-rays.