Department of Radiation Oncology, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229, USA.
Med Phys. 2013 Jul;40(7):071731. doi: 10.1118/1.4812415.
In this study, the authors are evaluating a new, commercially available 2D array that offers 3D dose reconstruction for patient specific intensity modulated radiation therapy quality assurance (IMRT QA).
The OCTAVIUS 4D system and its accompanying software (VERISOFT) by PTW were evaluated for the accuracy of the dose reconstruction for patient specific pretreatment IMRT QA. OCTAVIUS 4D measures the dose plane at the linac isocenter as the phantom rotates synchronously with the gantry, maintaining perpendicularity with the beam, by means of an inclinometer and a motor. The measurements collected during a volumetric modulated arc therapy delivery (VMAT) are reconstructed into a 3D dose volume. The VERISOFT application is used to perform the analysis, by comparing the reconstructed dose against the 3D dose matrix from the treatment planning system (TPS) that is computed for the same geometry and beam arrangement as that of the measurement. In this study, the authors evaluated the 3D dose reconstruction algorithm of this new system using a series of tests. Using the Octavius 4D phantom as the patient, dose distributions for various field sizes, beam orientations, shapes, and combination of fields were calculated using the Pinnacle3, TPS, and the respective DICOMRT dose was exported to the VERISOFT analysis software. Measurements were obtained by delivering the test treatment plans and comparisons were made based on gamma index, dose profiles, and isodose distribution analysis. In addition, output factors were measured and the dose linearity of the array was assessed. Those measurements were compared against measurements in water using a single, calibrated ionization chamber as well as calculations from Pinnacle for the same delivery geometries.
The number of voxels that met the 3%/3 mm criteria for the volumetric 3D gamma index analysis ranged from 92.3% to 98.9% for all the patient plans that the authors evaluated. 2D gamma analysis in the axial, sagittal, and coronal planes produced similar results to those in the 3D gamma analysis. The new detector system does not require an angular dependence correction because it rotates in synchrony with the gantry and the detector array maintains a constant SAD while always perpendicular to the beam axis. Output factors were within 2% when compared to ionization chamber measurements and Pinnacle calculations. Similar agreement was observed when testing the MU linearity (for MU values above 2) as well as dose rate effect.
The OCTAVIUS 4D system has some unique characteristics that can potentially improve the patient specific pretreatment IMRT QA data collection and analysis. The ability of the software to reconstruct from the measurements the true 3D dose distribution in the phantom, provides a unique perspective for the medical physicist that evaluates a patient's QA plan.
在这项研究中，作者评估了一种新的商用 2D 阵列，该阵列可用于患者特定强度调制放射治疗质量保证（IMRT QA）的 3D 剂量重建。
作者评估了由 PTW 生产的 OCTAVIUS 4D 系统及其配套软件（VERISOFT）在患者特定预处理 IMRT QA 中的剂量重建准确性。OCTAVIUS 4D 通过测斜仪和电机，在射束同步旋转时，在直线加速器等中心测量剂量平面，保持与射束垂直。在容积调强弧形治疗（VMAT）的输送过程中收集的测量结果被重建为 3D 剂量体积。VERISOFT 应用程序通过将重建剂量与治疗计划系统（TPS）计算的 3D 剂量矩阵进行比较来执行分析，该矩阵是针对与测量相同的几何形状和射束排列计算的。在这项研究中，作者使用一系列测试评估了该新系统的 3D 剂量重建算法。使用 Octavius 4D 体模作为患者，使用 Pinnacle3、TPS 计算了各种射野大小、射束方向、形状和射野组合的剂量分布，并将各自的 DICOMRT 剂量导出到 VERISOFT 分析软件。通过输送测试治疗计划获得测量结果，并基于伽马指数、剂量分布和等剂量分布分析进行比较。此外，还测量了输出因子，并评估了阵列的剂量线性度。将这些测量值与使用单个校准电离室进行的水中测量值以及针对相同输送几何形状的 Pinnacle 计算值进行了比较。
作者评估的所有患者计划中，符合体积 3D 伽马指数分析 3%/3mm 标准的体素数量范围为 92.3%至 98.9%。轴向、矢状和冠状平面的 2D 伽马分析产生了与 3D 伽马分析相似的结果。新的探测器系统不需要角度依赖性校正，因为它与旋转龙门架同步旋转，并且探测器阵列在始终垂直于射束轴的情况下保持恒定的源轴距。与电离室测量值和 Pinnacle 计算值相比，输出因子在 2%以内。在测试 MU 线性度（对于高于 2 的 MU 值）以及剂量率效应时，也观察到了类似的一致性。
OCTAVIUS 4D 系统具有一些独特的特性，可能会改善患者特定预处理 IMRT QA 的数据收集和分析。软件能够从测量结果中重建体模中的真实 3D 剂量分布，为评估患者 QA 计划的医学物理学家提供了独特的视角。
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