Department of Radiation Oncology, University of Illinois, Chicago, IL, USA.
Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL, USA.
J Appl Clin Med Phys. 2019 Aug;20(8):21-28. doi: 10.1002/acm2.12672. Epub 2019 Jul 22.
Single-isocenter volumetric modulated arc therapy (VMAT) technique can provide stereotactic radiosurgery (SRS) treatment with improved delivery efficiency for treating multiple metastases. Nevertheless, planning is time consuming and verification of frame-based SRS setup, especially at noncoplanar angles, can be challenging. We report on a single-isocenter VMAT technique with a special focus on improving treatment workflow and delivery verification to exploit the minimized patient motion of the frame-based SRS. We developed protocols for preplanning and verification for VMAT and evaluated them for ten patient cases. Preplans based on MRI were used to generate comparable treatment plans using CT taken on the day of treatment after frame placement. Target positioning accuracy was evaluated by stereoscopic in-room kV imaging. Dosimetric accuracy of the noncoplanar plan delivery was validated using measurement-guided 3D dose reconstruction as well as film-based end-to-end test with a Rando phantom. Average absolute differences of homogeneity indices, conformity indices, and V12Gy between MR preplans and CT-based plans were within 5%. In-room imaging positioning accuracy of 0.4 mm was verified to be independent of the distance to the isocenter. For treatment verification, average local and global passing rates of the 3D gamma (1 mm, 3%) were 86% and 99%, respectively. D99 values were matched within 5% for individual target structures (>0.5 cc). Additional film analysis confirmed dosimetric accuracy for small targets that had large verification errors in the 3D dose reconstruction. Our results suggest that the advantages of frame-based SRS and noncoplanar single-isocenter VMAT technique can be combined for efficient and accurate treatment of patients with multiple metastases.
单中心容积旋转调强放疗（VMAT）技术可以提供立体定向放射外科（SRS）治疗，提高治疗多发性转移瘤的输送效率。然而，计划时间较长，并且基于框架的 SRS 设置的验证（尤其是在非共面角度）具有挑战性。我们报告了一种单中心 VMAT 技术，特别关注改善治疗工作流程和输送验证，以利用基于框架的 SRS 最小化的患者运动。我们为 VMAT 制定了预规划和验证方案，并对 10 例患者病例进行了评估。使用 MRI 进行预规划，以生成基于 CT 的治疗计划，该 CT 是在框架放置后治疗当天拍摄的。通过立体室内千伏成像评估目标定位准确性。使用测量引导的 3D 剂量重建以及 Rando 体模的胶片端到端测试验证非共面计划输送的剂量准确性。MR 预计划和 CT 计划之间均匀性指数、适形性指数和 V12Gy 的平均绝对差异在 5%以内。室内成像定位精度为 0.4mm，被验证与到等中心的距离无关。对于治疗验证，3D 伽马（1mm，3%）的局部和全局通过率平均值分别为 86%和 99%。个别靶结构（>0.5cc）的 D99 值匹配度在 5%以内。额外的胶片分析证实了小靶区的剂量准确性，这些靶区在 3D 剂量重建中存在较大的验证误差。我们的结果表明，基于框架的 SRS 和非共面单中心 VMAT 技术的优势可以结合起来，为多发性转移瘤患者提供高效、准确的治疗。
