宫颈癌容积调强计划验证中伽马通过率最佳阈值研究

目的 面向宫颈癌容积调强计划验证,基于Delta 4三维剂量验证系统,探寻在不同的伽马分析基准(百分剂量差异/一致性距离差异)下评判计划实施的最佳通过率阈值。方法 选取30例经临床批准的双弧容积调强(采用瓦里安RapidArc^TM技术)宫颈癌计划,利用Delta 4对其进行伽马分析和DVH评价。根据两个准则对全部计划进行分类:①DVH上所有特定剂量学指标的绝对百分剂量差异<5%视为临床可接受计划;②在2%/2 mm、3%/3 mm基准下伽马通过率超过90%或95%视为计划通过。基于此分类结果进行敏感性和特异性分析,并绘制受试者工作特征曲线(ROC),通过计算约登系数的方式寻找不同伽马分析基准(全局与局部2%/2 mm和3%/3 mm)条件下的最佳通过率阈值,最后通过分析敏感性和特异性来定量比较在常规阈值(90%和95%)和最佳阈值处区分计划是否能被临床接受的能力大小。结果 全局3%/3 mm和2%/2 mm基准下的最佳阈值点分别为98.3%和87.05%;局部相同基准下的最佳阈值点分别为97.55%和86.05%。在3%/3 mm测量基准下,最佳阈值相比于常规阈值(90%和95%)而言其全局和局部伽马敏感性可以达到0.93;而在2%/2 mm测量基准下最佳阈值的全局伽马敏感性为0.65,特异性为0.49;局部伽马敏感性为0.70,特异性为0.46,敏感性和特异性更为平衡。结论 利用最佳阈值点判别治疗计划是否通过可让敏感性和特异性之间取得较好平衡,一定程度上减少了不可接受计划因漏判给患者带来危害机会,同时降低了可接受计划因误判而增加物理师日常工作量概率。

Study of the optimal thresholds of gamma passing rate in VMAT plan verification for cervical cancer

Objective To investigate the optimal thresholds of the passing rate with different gamma measurement criteria (percent dose difference/DTA) based on the Delta 4 three-dimensional dosimetric verification system in the verification of volumetric modulated arc-therapy (VMAT) plan for cervical cancer. Methods Thirty clinically-approved dual-arc VMAT plans using the RapidArcTM (Varian Medical Systems Inc.) for cervical cancer were randomly selected. The gamma analysis and dose-volume histogram (DVH) evaluation were performed using Delta 4. All the plans were classified according to the following two criteria:1. If the absolute percentage dose errors of all specific dosimetry indices on the DVH were less than 5%,the plan was regarded as clinically acceptable. 2. If the gamma passing rate was 90% or 95% under the criteria of 2%/2 mm and 3%/3 mm,the plan was regarded as acceptable. The sensitivity and specificity analyses were conducted based on the classification results and the receiver operating characteristic (ROC) curve was plotted. By calculating the Youden Index,the optimal thresholds under different Gamma criteria (global and local 2%/2 mm and 3%/3 mm) were investigated. Finally,the ability of distinguishing the plan was clinically acceptable or not between the conventional and optimal thresholds was quantitatively compared according to the sensitivity and specificity analyses. Results The optimal thresholds under the global 3%/3 mm and 2%/2 mm criteria were 98.3% and 87.05%;and 97.55%、86.05% for the local gamma analysis. Compared with the conventional thresholds,the sensitivity of the optimal thresholds was 0.93 by using the global and local gamma analyses under the 3%/3 mm criterion. Under the 2%/2 mm criterion,the sensitivity of the optimal thresholds was 0.65 and the specificity was 0.49 by using the global gamma analysis. The sensitivity was 0.7 and the specificity was 0.46 by using the local gamma analysis,suggesting that the sensitivity and the specificity were more balanced under the 2%/2 mm criterion. Conclusions Application of the optimal thresholds in the verification of VMAT plans can maintain the balance between the sensitivity and specificity,prevent the harm of clinically unacceptable plans to patients to certain extent and reduce the probability of increasing the daily work load for physicists due to the misjudgement of clinically acceptable plans.