目的:使用基于蒙特卡罗(MC)的剂量验证软件,阐明基于模型的算法在采用螺旋断层放射治疗(HT)的肺立体定向放射治疗(SBRT)中引起的剂量误差。
方法:对于38个肺SBRT计划,将HT的治疗计划系统(TPS)的剂量计算精度与DoseCHECK的结果进行比较,基于MC的商用独立验证软件。提取以下指标来评估剂量测定误差的相关性:(1)目标体积,(2)计划目标体积(PTV)边缘的平均计算机断层扫描(CT)值,(3)PTV周围2mm区域的平均CT值(PTV环)。接收器工作特性(ROC)分析确定了PTVD95%差异的5%的阈值。然后,根据ROC分析这3项指标的临界值,将38项计划分为两组.使用Mann-WhitneyU检验对组间的剂量学差异进行统计学比较。
结果:在38个计划中的16个计划中,在PTVD95%中,HT的TPS高估了5%以上。PTV环显示出与剂量学差异最强的相关性。目标体积的截止值,PTV边缘,PTV环是14.7cc,-754HU,和-708HU,分别。目标体积的曲线下面积(AUC),PTV边缘,PTV环分别为0.835、0.878和0.932。当PTV体积小于15cc或靶周围的CT值小于-700HU时,观察到超过5%的剂量误差。
结论:如果本研究中的三个指标低于阈值,HT的TPS可能会高估PTV剂量超过5%。因此,对于HT患者的肺部SBRT,强烈建议使用基于MC的算法进行独立验证.
OBJECTIVE: 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.
METHODS: 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 D95%. 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.
RESULTS: TPS of HT overestimated by more than 5% in the PTV D95% 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.
CONCLUSIONS: 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.