Physics and Astronomy Department, Rice University, MS 315, 6100 Main Street, Houston, TX 77005, United States of America. Department of Radiation Physics, Unit 1202, The University of Texas M. D. Anderson Cancer, 1515 Holcombe Blvd., Houston, TX 77030, United States of America. Author to whom any correspondence should be addressed.
Phys Med Biol. 2018 Feb 9;63(4):045003. doi: 10.1088/1361-6560/aaa845.
To evaluate the effect of approximations in clinical analytical calculations performed by a treatment planning system (TPS) on dosimetric indices in intensity modulated proton therapy. TPS calculated dose distributions were compared with dose distributions as estimated by Monte Carlo (MC) simulations, calculated with the fast dose calculator (FDC) a system previously benchmarked to full MC. This study analyzed a total of 525 patients for four treatment sites (brain, head-and-neck, thorax and prostate). Dosimetric indices (D02, D05, D20, D50, D95, D98, EUD and Mean Dose) and a gamma-index analysis were utilized to evaluate the differences. The gamma-index passing rates for a 3%/3 mm criterion for voxels with a dose larger than 10% of the maximum dose had a median larger than 98% for all sites. The median difference for all dosimetric indices for target volumes was less than 2% for all cases. However, differences for target volumes as large as 10% were found for 2% of the thoracic patients. For organs at risk (OARs), the median absolute dose difference was smaller than 2 Gy for all indices and cohorts. However, absolute dose differences as large as 10 Gy were found for some small volume organs in brain and head-and-neck patients. This analysis concludes that for a fraction of the patients studied, TPS may overestimate the dose in the target by as much as 10%, while for some OARs the dose could be underestimated by as much as 10 Gy. Monte Carlo dose calculations may be needed to ensure more accurate dose computations to improve target coverage and sparing of OARs in proton therapy.
评估治疗计划系统 (TPS) 进行的临床分析计算中的近似值对强度调制质子治疗中剂量学指标的影响。将 TPS 计算的剂量分布与通过蒙特卡罗 (MC) 模拟估算的剂量分布进行比较，使用先前与全 MC 基准的快速剂量计算器 (FDC) 进行计算。这项研究共分析了四个治疗部位（脑部、头颈部、胸部和前列腺）的 525 名患者。利用剂量学指标 (D02、D05、D20、D50、D95、D98、EUD 和平均剂量) 和伽马指数分析来评估差异。对于剂量大于最大剂量 10%的体素，3%/3 mm 标准的伽马指数通过率对于所有部位的中位数均大于 98%。对于所有病例，对于靶区的所有剂量学指标，中位数差异均小于 2%。然而，在 20%的胸部患者中发现了靶区差异高达 10%的情况。对于危及器官 (OARs)，对于所有指标和队列，中位数绝对剂量差异均小于 2 Gy。然而，在一些脑部和头颈部患者的小体积器官中，发现了高达 10 Gy 的绝对剂量差异。该分析得出结论，对于研究中的一部分患者，TPS 可能会高估靶区的剂量多达 10%，而对于一些 OARs，剂量可能会低估多达 10 Gy。为了确保更准确的剂量计算，以改善质子治疗中靶区的覆盖和 OAR 的保护，可能需要进行蒙特卡罗剂量计算。
