Pan Yuxi, Yang Ruijie, Li Jun, Zhang Xile, Liu Lu, Wang Junjie
Department of Radiation Oncology, Peking University Third Hospital, Beijing, China.
J Appl Clin Med Phys. 2018 May;19(3):142-148. doi: 10.1002/acm2.12314. Epub 2018 Mar 30.
Monte Carlo (MC) simulation, as the most accurate dose calculation algorithm, is available in the MultiPlan treatment planning system for Cyberknife. The main purpose of this work was to perform experiments to thoroughly investigate the accuracy of the MC dose calculation algorithm. Besides the basic MC beam commissioning, two test scenarios were designed. First, single beam tests were performed with a solid water phantom to verify the MC source model in simple geometry. Then, a lung treatment plan on a CIRS thorax phantom was created to mimic the clinical patient treatment. The plan was optimized and calculated using ray tracing (RT) algorithm and then recalculated using MC algorithm. Measurements were performed in both a homogeneous phantom and a heterogeneous phantom (CIRS). Ion-chamber and radiochromic film were used to obtain absolute point dose and dose distributions. Ion-chamber results showed that the differences between measured and MC calculated dose were within 3% for all tests. On the film measurements, MC calculation results showed good agreements with the measured dose for all single beam tests. As for the lung case, the gamma passing rate between measured and MC calculated dose was 98.31% and 97.28% for homogeneous and heterogeneous situation, respectively, using 3%/2 mm criteria. However, RT algorithm failed with the passing rate of 79.25% (3%/2 mm) for heterogeneous situation. These results demonstrated that MC dose calculation algorithm in the Multiplan system is accurate enough for patient dose calculation. It is strongly recommended to use MC algorithm in heterogeneous media.
蒙特卡罗（MC）模拟作为最精确的剂量计算算法，可用于赛博刀的MultiPlan治疗计划系统中。这项工作的主要目的是进行实验，全面研究MC剂量计算算法的准确性。除了基本的MC射束调试外，还设计了两个测试场景。首先，使用固体水模体进行单束测试，以在简单几何形状中验证MC源模型。然后，在CIRS胸部模体上创建一个肺部治疗计划，以模拟临床患者治疗。该计划使用射线追踪（RT）算法进行优化和计算，然后使用MC算法重新计算。在均匀模体和非均匀模体（CIRS）中均进行了测量。使用电离室和放射变色胶片来获得绝对点剂量和剂量分布。电离室结果表明，所有测试中测量剂量与MC计算剂量之间的差异均在3%以内。在胶片测量中，MC计算结果与所有单束测试的测量剂量显示出良好的一致性。对于肺部病例，使用3%/2 mm标准时，均匀和非均匀情况下测量剂量与MC计算剂量之间的伽马通过率分别为98.31%和97.28%。然而，RT算法在非均匀情况下的通过率为79.25%（3%/2 mm），未通过。这些结果表明，Multiplan系统中的MC剂量计算算法对于患者剂量计算足够准确。强烈建议在非均匀介质中使用MC算法。
