Department of Radiation Oncology, School of Medicine, Cancer Therapy and Research Center at the University of Texas Health Science Center San Antonio, San Antonio, TX 78229, USA.
Technol Cancer Res Treat. 2012 Feb;11(1):69-82. doi: 10.7785/tcrt.2012.500236.
The purpose of this study is to evaluate 3D dose reconstruction of pretreatment verification plans using multiple 2D planes acquired from the OCTAVIUS phantom and the Seven29 detector array. Eight VMAT patient treatment plans of different sites were delivered onto the OCTAVIUS phantom. The plans span a variety of tumor site locations from low to high plan complexity. A patient specific quality assurance (QA) plan was created and delivered for each of the 8 patients using the OCTAVIUS phantom in which the Seven29 detector array was placed. Each plan was delivered four times by rotating the phantom in 45° increments along its longitudinal axis. The treatment plans were delivered using a Novalis Tx with the HD120 MLC. Each of the four corresponding planar doses was exported as a text file for further analysis. An in-house MATLAB code was used to process the planar dose information. A cylindrical geometry-based, linear interpolation method was utilized to generate the measured 3D dose reconstruction. The TPS calculated volumetric dose was exported and compared against the measured reconstructed volumetric dose. Dose difference, dose area histograms (DAH), isodose lines, profiles, 2D and 3D gamma were used for evaluation. The interpolation method shows good agreement (<2%) between the planned dose distributions in the high dose region but shows discrepancies in the low dose region. Horizontal profiles, dose area histograms and isodose lines show good agreement for the sagittal and coronal planes but demonstrate slight discrepancies in the transverse plane. The 3D gamma index average was 92.4% for all patients when a 5%/5 mm gamma passing rate criteria was employed but dropped to <80.1% on average when parameters were reduced to 2%/2 mm. A simple cylindrical geometry-based, linear interpolation method is able to predict good agreement in the high dose region between the reconstructed volumetric dose and the planned volumetric dose. It is important to mention that the interpolation algorithm introduces dose discrepancies in small regions within the high dose gradients due to the interpolation itself. However, the work presented serves as a good starting point to establish a benchmark for the level of manipulation necessary to obtain 3D dose delivery quality assurance using current technology.
本研究旨在评估使用 OCTAVIUS 体模和 Seven29 探测器阵列获取的多个 2D 平面来重建预处理验证计划的 3D 剂量。将 8 个不同部位的 VMAT 患者治疗计划输送到 OCTAVIUS 体模上。这些计划涵盖了从低到高计划复杂性的各种肿瘤部位。为 8 名患者中的每一位创建并提供了特定于患者的质量保证（QA）计划，其中在 OCTAVIUS 体模中放置了 Seven29 探测器阵列。通过将体模沿其纵轴以 45°的增量旋转四次，每次输送一个计划。治疗计划使用 Novalis Tx 和 HD120 MLC 输送。将四个相应的平面剂量中的每一个导出为一个文本文件以进行进一步分析。使用内部 MATLAB 代码处理平面剂量信息。使用基于圆柱几何形状的线性插值方法生成测量的 3D 剂量重建。导出 TPS 计算的体积剂量，并将其与测量的重建体积剂量进行比较。使用剂量差异、剂量面积直方图（DAH）、等剂量线、轮廓、2D 和 3D 伽马进行评估。插值方法在高剂量区域中计划剂量分布之间显示出良好的一致性（<2%），但在低剂量区域中显示出差异。矢状面和冠状面的水平轮廓、剂量面积直方图和等剂量线显示出良好的一致性，但在横断面显示出轻微的差异。当采用 5%/5mm 伽马通过率标准时，所有患者的 3D 伽马指数平均值为 92.4%，但当参数降低到 2%/2mm 时，平均值降至<80.1%。基于简单的圆柱几何形状的线性插值方法能够在重建的体积剂量和计划的体积剂量之间在高剂量区域中预测出良好的一致性。需要提到的是，由于插值本身，插值算法会在高剂量梯度内的小区域中引入剂量差异。然而，所呈现的工作为使用当前技术获得 3D 剂量输送质量保证所需的操作水平建立基准提供了一个良好的起点。
