基于ArcCHECK模体的VMAT计划验证及摆位误差对剂量验证的影响

VMAT plan verification based on ArcCHECK phantom and the effects of setup error on dose verification

目的:探究ArcCHECK模体在旋转容积调强技术(VMAT)计划验证中的应用,并利用软件模拟摆位误差对剂量验证的影响。方法:随机收集45例VMAT计划,分别选取胸部肿瘤、乳腺癌和宫颈癌各15例,将ArcCHECK模体实测的剂量分布与计划系统计算的结果进行对比分析,分别探究在阈值10%下,3%/3 mm和2%/2 mm时,Gamma分析与DTA分析下相对剂量(RD)与绝对剂量(AD)的通过率。利用SUNnuclear公司Sunpatient软件将计划系统计算的剂量分布与实际测量的剂量分布进行对比,并利用软件模拟旋转误差,分别旋转±0.5°、±1°、±1.5°、±2°,将旋转后的剂量分布与计划系统计算剂量分布对比,得到旋转误差下的计划验证通过率;同样利用软件模拟平移误差,分别向X、Y方向平移±1、±2、±3、±5 mm后进行剂量分布对比,得到平移误差下的计划验证通过率。结果:当阈值选择10%、3%/3 mm时,Gamma分析时,RD与AD下各部位的通过率基本达到95%及以上,DTA分析时,RD和AD下各部位的通过率基本达到90%及以上。当阈值选择10%、2%/2 mm时,各部位肿瘤VMAT计划的验证通过率无论在Gamma还是DTA分析时,RD和AD的平均通过率只有80%左右。存在误差时,旋转误差大于等于1°时,各部位肿瘤VMAT计划验证在两种分析方法下通过率的单因素方差分析结果显示P<0.05;X方向和Y方向平移误差大于等于3 mm时,单因素方差分析结果显示P<0.05。结论:ArcCHECK模体能很好地应用于VMAT计划的验证,阈值选择10%、3%/3 mm时,胸部肿瘤、乳腺癌和宫颈癌验证通过率均能达到95%及以上;阈值选择10%、2%/2 mm时通过率均有大幅度下降,仅有80%左右。旋转误差大于等于1°时对计划验证通过率有显著影响,差异具有统计学意义,同样X方向或Y方向平移误差大于等于3 mm时,两种分析方法下的计划验证通过率均有显著差异。

Objective To explore the application of ArcCHECK phantom in volumetric modulated arc therapy(VMAT) plan verification, and to simulate the effects of setup error on dose verification by software. Methods A total of 45 VMAT plans were randomly collected, including 15 cases of chest tumors, 15 cases of breast cancer and 15 cases of cervical cancer. The dose distribution measured by Arc CHECK phantom was compared with the calculated result of planning system for analyzing the passing rates of relative dose(RD) and absolute dose(AD) under Gamma analysis and DTA analysis with the threshold at 10%, 3%/3 mm and 2%/2 mm. The Sunpatient software from SUNnuclear was used to compare the dose distribution calculated by planning system with the measured dose distribution and to simulate rotation errors by rotating ±0.5°, ±1°, ±1.5°, ±2°, respectively. The passing rate of plan verification under rotation errors was obtained by comparing the dose distribution after rotation and the dose distribution calculated by planning system. The software was also used to simulate translation errors. The passing rate of plan verification under translation errors was obtained by comparing the dose distribution after shifting ±1, ±2, ±3, ±5 mm to the X and Y directions,respectively, and the calculated results. Results When the threshold was selected at 10%, 3%/3 mm, the passing rate of RD and AD in VMAT plans for different cancer was basically up to or higher than 95% in Gamma analysis and 90% in DTA analysis. When the threshold was selected at 10%, 2%/2 mm, the average passing rates of RD and AD in VMAT plan for different cancer were only about 80% whether in Gamma analysis or DTA analysis. When the rotation error was greater than or equal to 1°, the one-way ANOVA on the passing rate of VMAT plan verification by two analysis methods showed that the P value was less than 0.05. When the translation errors in X and Y directions were greater than or equal to 3 mm, one-way ANOVA showed that the P values were also less than 0.05. Conclusion Arc CHECK phantom can be well applied to VMAT plan verification. With the threshold at 10%,3%/3 mm, the passing rate of the verification of VMAT plans for chest tumors, breast cancer and cervical cancer is up to or higher than 95%, but the passing rate is dropped to about 80% when the threshold was set at 10%, 2%/2 mm. The rotation error which is greater than or equal to 1° has a significant effect on the passing rate of plan verification, with statistical differences. When the translation errors in X or Y directions are greater than or equal to 3 mm, there are significant differences in the passing rate of plan verification between two analysis methods.