Juntendo University Graduate School of Medicine, Bunkyo-ku, Tokyo, Japan.
Department of Radiology, Juntendo University Urayasu Hospital, Urayasu-shi, Chiba, Japan.
J Appl Clin Med Phys. 2024 May;25(5):e14305. doi: 10.1002/acm2.14305. Epub 2024 Feb 18.
To elucidate the dosimetric errors caused by a model-based algorithm in lung stereotactic body radiation therapy (SBRT) with Helical TomoTherapy (HT) using Monte Carlo (MC)-based dose verification software.
For 38 plans of lung SBRT, the dose calculation accuracy of a treatment planning system (TPS) of HT was compared with the results of DoseCHECK, the commercial MC-based independent verification software. The following indices were extracted to evaluate the correlation of dosimetric errors: (1) target volume, (2) average computed tomography (CT) value of the planning target volume (PTV) margin, and (3) average CT value of surrounding 2-mm area of the PTV (PTV ring). Receiver operating characteristic (ROC) analyses determined the threshold for 5% of differences in PTV D. Then, the 38 plans were classified into two groups using the cutoff values of ROC analysis for these three indices. Dosimetric differences between groups were statistically compared using the Mann-Whitney U test.
TPS of HT overestimated by more than 5% in the PTV D in 16 of 38 plans. The PTV ring showed the strongest correlation with dosimetric differences. The cutoff value for the target volume, the PTV margin, and the PTV ring was 14.7 cc, -754 HU, and -708 HU, respectively. The area under the curve (AUC) for the target volume, the PTV margin, and the PTV ring were 0.835, 0.878, and 0.932, respectively. Dosimetric errors more than 5% were observed when the PTV volume was less than 15 cc or when the CT value around the target was less than -700 HU.
The TPS of HT might overestimate the PTV dose by more than 5% if any the three indices in this study were below threshold. Therefore, independent verification with an MC-based algorithm should be strongly recommended for lung SBRT in HT.
使用基于蒙特卡罗（MC）的剂量验证软件阐明螺旋断层放疗（HT）中基于模型的算法在肺部立体定向体部放疗（SBRT）中引起的剂量学误差。
对于 38 例肺部 SBRT 计划，比较了 HT 治疗计划系统（TPS）的剂量计算准确性与商业 MC 独立验证软件 DoseCHECK 的结果。提取以下指标评估剂量学误差的相关性：（1）靶区；（2）计划靶区（PTV）边界的平均 CT 值；（3）PTV 环周围 2mm 区域的平均 CT 值。接收者操作特性（ROC）分析确定 PTV D 差异 5%的阈值。然后，使用 ROC 分析的三个指标的截止值将 38 个计划分为两组。使用 Mann-Whitney U 检验对两组间的剂量差异进行统计学比较。
HT 的 TPS 在 38 个计划中有 16 个超过 PTV D 的 5%。PTV 环与剂量差异相关性最强。靶区、PTV 边界和 PTV 环的截止值分别为 14.7cc、-754HU 和-708HU。靶区、PTV 边界和 PTV 环的曲线下面积（AUC）分别为 0.835、0.878 和 0.932。当 PTV 体积小于 15cc 或靶区周围 CT 值小于-700HU 时，会观察到剂量误差超过 5%。
如果本研究中的三个指标中的任何一个低于阈值，HT 的 TPS 可能会高估 PTV 剂量超过 5%。因此，对于 HT 中的肺部 SBRT，强烈推荐使用基于 MC 的算法进行独立验证。
