使用 EPID 剂量测定进行实时肿瘤跟踪治疗的 4D 体内剂量验证。

4D in vivo dose verification for real-time tumor tracking treatments using EPID dosimetry.

机构信息

Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada; Medical Physics Department, CancerCare Manitoba, 675 McDermot Avenue, Winnipeg, Manitoba R3E 0V9, Canada.

Medical Physics Department, CancerCare Manitoba, 675 McDermot Avenue, Winnipeg, Manitoba R3E 0V9, Canada.

出版信息

Med Dosim. 2021;46(1):29-38. doi: 10.1016/j.meddos.2020.07.003. Epub 2020 Aug 7.

DOI:10.1016/j.meddos.2020.07.003

PMID:32778520

Abstract

The use of sophisticated techniques such as gating and tracking treatments requires additional quality assurance to mitigate increased patient risks. To address this need, we have developed and validated an in vivo method of dose delivery verification for real-time aperture tracking techniques, using an electronic portal imaging device (EPID)-based, on-treatment patient dose reconstruction and a dynamic anthropomorphic phantom. Using 4DCT scan of the phantom, ten individual treatment plans were created, 1 for each of the 10 separate phases of the respiratory cycle. The 10 MLC apertures were combined into a single dynamic intensity-modulated radiation therapy (IMRT) plan that tracked the tumor motion. The tumor motion and linac delivery were synchronized using an RPM system (Varian Medical Systems) in gating mode with a custom breathing trace. On-treatment EPID frames were captured using a data-acquisition computer with a dedicated frame-grabber. Our in-house EPID-based in vivo dose reconstruction model was modified to reconstruct the 4D accumulated dose distribution for a dynamic MLC (DMLC) tracking plan using the 10-phase 4DCT dataset. Dose estimation accuracy was assessed for the DMLC tracking plan and a single-phase (50% phase) static tumor plan, represented a static field test to verify baseline accuracy. The 3%/3 mm chi-comparison between the EPID-based dose reconstruction for the static tumor delivery and the TPS dose calculation for the static plan resulted in 100% pass rate for planning target volume (PTV) voxels while the mean percentage dose difference was 0.6%. Comparing the EPID-based dose reconstruction for the DMLC tracking to the TPS calculation for the static plan gave a 3%/3 mm chi pass rate of 99.3% for PTV voxels and a mean percentage dose difference of 1.1%. While further work is required to assess the accuracy of this approach in more clinically relevant situations, we have established clinical feasibility and baseline accuracy of using the transmission EPID-based, in vivo patient dose verification for MLC-tracking treatments.

摘要

使用门控和跟踪治疗等复杂技术需要额外的质量保证，以降低增加的患者风险。为满足这一需求，我们开发并验证了一种用于实时孔径跟踪技术的体内剂量传递验证方法，该方法使用基于电子射野影像装置（EPID）的治疗中患者剂量重建和动态人体模型。通过对体模进行 4DCT 扫描，为每个呼吸周期的 10 个独立阶段分别创建了 10 个个体治疗计划。将 10 个 MLC 孔径组合成一个单独的动态调强放疗（IMRT）计划，以跟踪肿瘤运动。使用 RPM 系统（Varian Medical Systems）在门控模式下，通过定制呼吸轨迹使肿瘤运动和直线加速器输送同步。在治疗中使用带有专用帧抓取器的数据采集计算机捕获 EPID 帧。我们的内部基于 EPID 的体内剂量重建模型经过修改，可使用 10 相位 4DCT 数据集为动态 MLC（DMLC）跟踪计划重建 4D 累积剂量分布。对 DMLC 跟踪计划和单相（50%相）静态肿瘤计划的剂量估计准确性进行了评估，这代表了对基线准确性的静态场测试。EPID 基于静态肿瘤输送的剂量重建与静态计划 TPS 剂量计算之间的 3%/3mm chi 比较，使计划靶区（PTV）体素的通过率达到 100%，而平均剂量差异百分比为 0.6%。将 DMLC 跟踪的 EPID 基于剂量重建与静态计划 TPS 计算进行比较，PTV 体素的 3%/3mm chi 通过率为 99.3%，平均剂量差异百分比为 1.1%。虽然需要进一步的工作来评估这种方法在更具临床相关性的情况下的准确性，但我们已经确定了使用基于传输 EPID 的体内患者剂量验证来进行 MLC 跟踪治疗的临床可行性和基线准确性。