Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany.
Z Med Phys. 2013 Feb;23(1):33-45. doi: 10.1016/j.zemedi.2012.08.002. Epub 2012 Aug 24.
A method to evaluate the dosimetric accuracy of volumetric modulated arc therapy (VMAT) treatment plans, generated with the MONACO™ (version 3.0) treatment planning system in realistic CT-data with an independent Geant4 based dose calculation algorithm is presented. Therefore a model of an Elekta Synergy linear accelerator treatment head with an MLCi2 multileaf collimator was implemented in Geant4. The time dependent linear accelerator components were modeled by importing either logfiles of an actual plan delivery or a DICOM-RT plan sequence. Absolute dose calibration, depending on a reference measurement, was applied. The MONACO as well as the Geant4 treatment head model was commissioned with lateral profiles and depth dose curves of square fields in water and with film measurements in inhomogeneous phantoms. A VMAT treatment plan for a patient with a thoracic tumor and a VMAT treatment plan of a patient, who received treatment in the thoracic spine region including metallic implants, were used for evaluation. MONACO, as well as Geant4, depth dose curves and lateral profiles of square fields had a mean local gamma (2%, 2mm) tolerance criteria agreement of more than 95% for all fields. Film measurements in inhomogeneous phantoms with a global gamma of (3%, 3mm) showed a pass rate above 95% in all voxels receiving more than 25% of the maximum dose. A dose-volume-histogram comparison of the VMAT patient treatment plans showed mean deviations between Geant4 and MONACO of -0.2% (first patient) and 2.0% (second patient) for the PTVs and (0.5±1.0)% and (1.4±1.1)% for the organs at risk in relation to the prescription dose. The presented method can be used to validate VMAT dose distributions generated by a large number of small segments in regions with high electron density gradients. The MONACO dose distributions showed good agreement with Geant4 and film measurements within the simulation and measurement errors.
介绍了一种在真实 CT 数据中使用独立的基于 Geant4 的剂量计算算法，评估由 MONACO™（版本 3.0）治疗计划系统生成的容积调强弧形治疗（VMAT）计划剂量准确性的方法。因此，在 Geant4 中实现了 Elekta Synergy 直线加速器治疗头和 MLCi2 多叶准直器的模型。通过导入实际计划交付的日志文件或 DICOM-RT 计划序列，对时间相关的直线加速器组件进行建模。进行了依赖于参考测量的绝对剂量校准。使用 MONACO 和 Geant4 治疗头模型对水立方野的侧向轮廓和深度剂量曲线以及不均匀体模中的胶片测量进行了验证。使用胸部长肿瘤的患者的 VMAT 治疗计划和在胸脊柱区域接受治疗的患者（包括金属植入物）的 VMAT 治疗计划对评估进行了评估。MONACO 和 Geant4 的方形野深度剂量曲线和侧向轮廓在所有场的平均局部伽马（2%，2mm）容限标准的符合率均超过 95%。在具有（3%，3mm）全局伽马的不均匀体模中的胶片测量在所有接收超过最大剂量 25%的体素中显示通过率超过 95%。对 VMAT 患者治疗计划的剂量-体积直方图进行比较，结果表明，对于 PTV，Geant4 和 MONACO 之间的平均偏差分别为-0.2%（第一个患者）和 2.0%（第二个患者），对于危及器官，分别为（0.5±1.0）%和（1.4±1.1）%与处方剂量相关。该方法可用于验证在具有高电子密度梯度的区域中由大量小片段生成的 VMAT 剂量分布。MONACO 剂量分布在模拟和测量误差范围内与 Geant4 和胶片测量结果具有良好的一致性。
