Parkview Comprehensive Cancer Center, Fort Wayne, IN 46845, USA.
J Appl Clin Med Phys. 2010 Jan 29;11(1):3142. doi: 10.1120/jacmp.v11i1.3142.
It is documented that well-modeled Monte Carlo dose calculation algorithms are more accurate than traditional correction-based algorithms or convolution algorithms at predicting dose distributions delivered to heterogeneous volumes. This increased accuracy has clinical implications for CyberKnife, particularly when comparing dose distributions between the ray-tracing and Monte Carlo algorithms. Differences between ray-tracing and Monte Carlo calculations are exacerbated for highly heterogeneous volumes and small field sizes. In this study, the anthropomorphic thorax phantom from the Radiological Physics Center was used to validate the accuracy of the CyberKnife Monte Carlo dose calculation algorithm. Retrospective comparisons of dose distributions calculated by ray-tracing and Monte Carlo were made for a selection of CyberKnife treatment plans; comparisons were based on target coverage and conformality. For highly heterogeneous cases, such as those involving the lungs, the ray-tracing algorithm consistently overestimated the target dose and coverage. In our sample of lung treatment plans, the average target coverage for ray-tracing calculations was 97.7%, while for Monte Carlo, the average coverage dropped to 69.2%. In each plan comparison, the same beam orientations and monitor units were used for both calculations. Significant changes in conformality were also observed. Isodose prescription lines and subsequent target coverage selected for treatment plans calculated with the ray-tracing algorithm may be different from comparable treatment plans calculated with Monte Carlo, and as such, may have clinical implications for dose prescriptions.
有文献记载，与传统的基于校正的算法或卷积算法相比，经过良好建模的蒙特卡罗剂量计算算法在预测不均匀体积的剂量分布方面更为准确。这种更高的准确性对 CyberKnife 具有临床意义，特别是在比较射线追踪和蒙特卡罗算法之间的剂量分布时。对于高度不均匀的体积和小射野尺寸，射线追踪和蒙特卡罗计算之间的差异会更加明显。在这项研究中，使用放射物理学中心的人体胸部模型来验证 CyberKnife 蒙特卡罗剂量计算算法的准确性。对选定的 CyberKnife 治疗计划的射线追踪和蒙特卡罗计算的剂量分布进行了回顾性比较；比较基于靶区覆盖和适形性。对于高度不均匀的情况，如涉及肺部的情况，射线追踪算法会一直高估靶区剂量和覆盖范围。在我们的肺部治疗计划样本中，射线追踪计算的平均靶区覆盖率为 97.7%，而蒙特卡罗的平均覆盖率降至 69.2%。在每个计划比较中，两种计算都使用相同的射束方向和监测单位。适形性也发生了显著变化。使用射线追踪算法计算的治疗计划的等剂量线和随后选择的靶区覆盖范围可能与使用蒙特卡罗计算的可比治疗计划不同，因此可能对剂量处方具有临床意义。
