Shine N S, Paramu Raghukumar, Gopinath M, Jaon Bos R C, Jayadevan P M
Department of Physics, Banasthali University, Jaipur, Rajasthan, India.
Division of Radiation Physics, Regional Cancer Center, Thiruvananthapuram, Kerala, India.
J Med Phys. 2019 Jul-Sep;44(3):156-175. doi: 10.4103/jmp.JMP_82_18.
The calculation accuracy of treatment planning systems (TPSs) drops drastically when the points outside the field edges are considered. The real accuracy of a TPS and linear accelerator (linac) combination for regions outside the field edge is a subject which demands more study. In this study, the accuracy of out-of-field dose calculated by a TPS, used with a TrueBeam (TB) linac, is quantified.
For dose calculation, Eclipse™ version 13.7 commissioned for TB machine was used. For comparison, Monte Carlo (MC) methods, as well as the measurements, were used. The VirtuaLinac, a Geant 4-based MC program which is offered as a cloud solution, is used for the generation of input phase-space (PS) files. This PS file was imported into PRIMO (PENELOPE based MC program) for the simulation of out-of-field dose.
In this study, the accuracy of the out-of-field dose calculated by a TPS for a TB linac was estimated. As per the results in comparison with MC simulations, the TPS underestimated the dose by around 45% on an average for the off-axis-distance range considered in this study. As the off-axis distance increased, the underestimation of the dose also increased.
In this work, it was observed that the TPS underestimates doses beyond the edges of treatment fields for a clinical treatment executed on a TB machine. This indicates that the out-of-field dose from TPSs should only be used with a clear understanding of the inaccuracy of dose calculations beyond the edge of the field.
当考虑射野边缘外的点时，治疗计划系统（TPS）的计算精度会大幅下降。TPS与直线加速器（直线加速器）组合对于射野边缘外区域的实际精度是一个需要更多研究的课题。在本研究中，对与TrueBeam（TB）直线加速器一起使用的TPS计算的野外剂量精度进行了量化。
剂量计算使用为TB机器调试的Eclipse™ 13.7版本。为了进行比较，使用了蒙特卡罗（MC）方法以及测量方法。VirtuaLinac是一个基于Geant 4的MC程序，作为云解决方案提供，用于生成输入相空间（PS）文件。该PS文件被导入PRIMO（基于PENELOPE的MC程序）以模拟野外剂量。
在本研究中，估计了TPS对TB直线加速器计算的野外剂量的精度。根据与MC模拟的结果，对于本研究中考虑的离轴距离范围，TPS平均低估剂量约45%。随着离轴距离的增加，剂量的低估也增加。
在这项工作中，观察到对于在TB机器上执行的临床治疗，TPS低估了治疗野边缘以外的剂量。这表明，只有在清楚了解射野边缘以外剂量计算不准确的情况下，才能使用TPS的野外剂量。
