Roche Michael, Crane Robert, Powers Marcus, Crabtree Timothy
The Department of Medical Physics, The Townsville Cancer Centre, Douglas, Queensland, Australia.
J Appl Clin Med Phys. 2018 Sep;19(5):473-482. doi: 10.1002/acm2.12399. Epub 2018 Jun 30.
The Monaco Monte Carlo treatment planning system uses three-beam model components to achieve accuracy in dose calculation. These components include a virtual source model (VSM), transmission probability filters (TPFs), and an x-ray voxel Monte Carlo (XVMC) engine to calculate the dose in the patient. The aim of this study was to assess the TPF component of the Monaco TPS and optimize the TPF parameters using measurements from an Elekta linear accelerator with an Agility™ multileaf collimator (MLC). The optimization began with all TPF parameters set to their default value. The function of each TPF parameter was characterized and a value was selected that best replicated measurements with the Agility™ MLC. Both vendor provided fields and a set of additional test fields were used to create a rigorous systematic process, which can be used to optimize the TPF parameters. It was found that adjustment of the TPF parameters based on this process resulted in improved point dose measurements and improved 3D gamma analysis pass rates with Octavius 4D. All plans calculated with the optimized beam model had a gamma pass rate of > 95% using criteria of 2% global dose/2 mm distance-to-agreement, while some plans calculated with the default beam model had pass rates as low as 88.4%. For measured point doses, the improvement was particularly noticeable in the low-dose regions of the clinical plans. In these regions, the average difference from the planned dose reduced from 4.4 ± 4.5% to 0.9 ± 2.7% with a coverage factor (k = 2) using the optimized beam model. A step-by-step optimization guide is provided at the end of this study to assist in the optimization of the TPF parameters in the Monaco TPS. Although it is possible to achieve good clinical results by randomly selecting TPF parameter values, it is recommended that the optimization process outlined in this study is followed so that the transmission through the TPF is characterized appropriately.
摩纳哥蒙特卡洛治疗计划系统使用三束模型组件来实现剂量计算的准确性。这些组件包括虚拟源模型（VSM）、传输概率滤波器（TPF）和X射线体素蒙特卡洛（XVMC）引擎，用于计算患者体内的剂量。本研究的目的是评估摩纳哥治疗计划系统的TPF组件，并使用配备Agility™多叶准直器（MLC）的医科达直线加速器的测量数据优化TPF参数。优化从将所有TPF参数设置为其默认值开始。对每个TPF参数的功能进行了表征，并选择了一个能最好地复制使用Agility™MLC测量结果的值。使用供应商提供的射野和一组额外的测试射野来创建一个严格的系统流程，该流程可用于优化TPF参数。结果发现，基于此流程调整TPF参数可改善点剂量测量结果，并提高使用Octavius 4D进行的三维伽马分析通过率。使用2%全局剂量/2毫米距离一致性标准时，所有使用优化射束模型计算的计划的伽马通过率均>95%，而一些使用默认射束模型计算的计划的通过率低至88.4%。对于测量的点剂量，在临床计划的低剂量区域改善尤为明显。在这些区域，使用优化射束模型时，与计划剂量的平均差异从4.4±4.5%降至0.9±2.7%，覆盖因子为（k=2）。本研究末尾提供了一份逐步优化指南，以协助优化摩纳哥治疗计划系统中的TPF参数。虽然随机选择TPF参数值也可能取得良好的临床效果，但建议遵循本研究中概述的优化过程，以便对通过TPF的传输进行适当表征。
