Department of Radiation Oncology, University of Minnesota, 420 Delaware Street Southeast, MMC-494, Minneapolis, Minnesota 55455, USA.
Med Phys. 2013 Aug;40(8):082101. doi: 10.1118/1.4813301.
With the recent introduction of intensity modulated arc therapy techniques, there is an increasing need for validation of treatment delivery in three-dimensional (3D) space. A commercial dosimetry device ArcCHECK™ (Sun Nuclear Corporation, Melbourne, FL, USA) can be used in conjunction with 3DVH program. With this system, one can reconstruct the 3D dose distribution produced in the actual patient. In this work the authors evaluate the relative accuracy of the ArcCHECK™-3DVH system using BANG3 (MGS Research, Guilford, CT, USA) polymer gel dosimeter.
About 15-cm diameter and 20-cm long cylindrical phantoms filled with BANG3 was used to simulate a patient, to which a volumetrically modulated arc therapy plan was created with Pinnacle3 treatment planning software (Philips Healthcare, Andover, MA, USA). The plan (76 Gy total in 38 fractions) was designed for prostate radiotherapy using a 6 MV photon beam from an Elekta Synergy linear accelerator (Elekta AB, Stockholm, Sweden). The treatment was delivered to the simulated patient. The same plan was used to irradiate an ArcCHECK™ device with an insert plug. The point dose at the isocenter was measured using a Farmer-type ionization chamber. The measured dose data were imported into the 3DVH program, which generated the 3D dose distributions projected onto the simulated patient. The dose data recorded in the polymer gel were read out using a MRI scanner and the 3D dose distribution delivered to the simulated patient was analyzed and compared with those from the 3DVH program and the Pinnacle3 software. The comparison was accomplished by using the gamma index, overlaying the isodose lines for a set of data on selected planes, and computing dose-volume histogram of structures.
The dose at the center of the ArcCHECK™ device measured with an ionization chamber was 1.82% lower than the dose predicted by Pinnacle3. The 3D dose distribution generated by Pinnacle3 was compared with those obtained by the ArcCHECK™-3DVH system and BANG3. The gamma passing rates for criteria of 3% dose difference, 3 mm distance-to-agreement, and 25% lower dose threshold were 99.1% for the former and 95.7% for the latter. The mean and maximum PTV doses estimated by the 3DVH were 74.0 and 79.3 Gy in comparison to 74.4 and 76.5 Gy with Pinnacle3. Those values for BANG3 measurements were 74.7 and 79.5 Gy. The mean doses to rectum were 40.2, 39.8, and 38.8 Gy for Pinnacle3, 3DVH, and BANG3, whereas the mean doses to the bladder were 26.7, 25.7, and 21.7 Gy, respectively.
The ArcCHECK™-3DVH system provides an accurate estimation of 3D dose distribution in an actual patient within a clinically meaningful tolerance level. However, both 3DVH and BANG3 showed two noticeable differences from Pinnacle3. First, the measured dose throughout the PTV region was less uniform than Pinnacle3. Second, the dose gradient at the interface between PTV and rectum was steeper than Pinnacle3 prediction. Further investigation may be able to identify the cause for these findings.
随着强度调制弧形治疗技术的最近引入，在三维（3D）空间中验证治疗传递的需求越来越大。商业剂量测定设备 ArcCHECK™（Sun Nuclear Corporation，佛罗里达州墨尔本，美国）可与 3DVH 程序一起使用。使用该系统，人们可以重建实际患者中产生的 3D 剂量分布。在这项工作中，作者使用 BANG3（MGS Research，康涅狄格州吉尔福德，美国）聚合物凝胶剂量计评估了 ArcCHECK™-3DVH 系统的相对准确性。
使用约 15 厘米直径和 20 厘米长的圆柱形体模填充 BANG3，以模拟患者，使用 Pinnacle3 治疗计划软件（飞利浦医疗保健，马萨诸塞州安多弗，美国）为其创建容积调制弧形治疗计划。该计划（76 Gy 总剂量分为 38 份）是为前列腺放射治疗设计的，使用来自 Elekta Synergy 线性加速器（Elekta AB，斯德哥尔摩，瑞典）的 6 MV 光子束。治疗被递送到模拟患者。相同的计划用于辐照具有插入塞的 ArcCHECK™设备。在等中心处使用 Farmer 型电离室测量点剂量。测量的剂量数据被导入 3DVH 程序，该程序生成投影到模拟患者上的 3D 剂量分布。记录在聚合物凝胶中的剂量数据使用 MRI 扫描仪读出，并分析和比较模拟患者上的 3D 剂量分布与来自 3DVH 程序和 Pinnacle3 软件的剂量分布。通过使用伽马指数、在选定平面上的一组数据的等剂量线叠加以及计算结构的剂量体积直方图来完成比较。
用电离室测量的 ArcCHECK™设备中心处的剂量比 Pinnacle3 预测的剂量低 1.82%。Pinnacle3 生成的 3D 剂量分布与通过 ArcCHECK™-3DVH 系统和 BANG3 获得的剂量分布进行了比较。对于 3%剂量差异、3 毫米距离协议和 25%较低剂量阈值的标准，前者的伽马通过率为 99.1%，后者为 95.7%。3DVH 估计的 PTV 平均和最大剂量分别为 74.0 和 79.3 Gy，而 Pinnacle3 为 74.4 和 76.5 Gy。BANG3 测量的相应值分别为 74.7 和 79.5 Gy。直肠的平均剂量为 40.2、39.8 和 38.8 Gy，膀胱的平均剂量分别为 26.7、25.7 和 21.7 Gy。
ArcCHECK™-3DVH 系统在临床有意义的容差范围内提供了实际患者中 3D 剂量分布的准确估计。然而，3DVH 和 BANG3 都与 Pinnacle3 有两个明显的差异。首先，整个 PTV 区域的测量剂量不如 Pinnacle3 均匀。其次，PTV 和直肠之间的剂量梯度比 Pinnacle3 预测的更陡峭。进一步的研究可能能够确定这些发现的原因。
