Université de Strasbourg, CNRS, IPHC UMR 7178, F-67000 Strasbourg, France.
Phys Med Biol. 2018 Jun 20;63(12):125018. doi: 10.1088/1361-6560/aac768.
The out-of-field dose in radiation therapy is a growing concern in regards to the late side-effects and secondary cancer induction. In high-energy x-ray therapy, the secondary neutrons generated through photonuclear reactions in the accelerator are part of this secondary dose. The neutron dose is currently not estimated by the treatment planning system while it appears to be preponderant for distances greater than 50 cm from the isocenter. Monte Carlo simulation has become the gold standard for accurately calculating the neutron dose under specific treatment conditions but the method is also known for having a slow statistical convergence, which makes it difficult to be used on a clinical basis. The neutron track length estimator, a neutron variance reduction technique inspired by the track length estimator method has thus been developped for the first time in the Monte Carlo code GATE to allow a fast computation of the neutron dose in radiotherapy. The details of its implementation, as well as the comparison of its performances against the analog MC method, are presented here. A gain of time from 15 to 400 can be obtained by our method, with a mean difference in the dose calculation of about 1% in comparison with the analog MC method.
在放射治疗中，越前野剂量是一个备受关注的问题，因为它与晚期副作用和继发癌症的诱导有关。在高能 X 射线治疗中，通过加速器中的光核反应产生的次级中子是这种次级剂量的一部分。目前，治疗计划系统并没有估算中子剂量，而对于离等中心 50 厘米以上的距离，中子剂量似乎更为突出。蒙特卡罗模拟已成为准确计算特定治疗条件下中子剂量的黄金标准，但该方法也因统计收敛缓慢而闻名，这使得它难以在临床上使用。因此，受轨迹长度估计方法启发，首次在蒙特卡罗代码 GATE 中开发了中子轨迹长度估计器，以允许在放射治疗中快速计算中子剂量。本文介绍了其实现细节，并与模拟 MC 方法的性能进行了比较。与模拟 MC 方法相比，我们的方法可以获得 15 到 400 倍的时间增益，剂量计算的平均差异约为 1%。
