Department of Radiation Oncology and Image-applied Therapy, Kyoto University Graduate School of Medicine, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan.
Division of Medical Physics, Department of Information Technology and Medical Engineering, Human Health Sciences, Graduate School of Medicine, Kyoto University, 53 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan.
J Radiat Res. 2020 Mar 23;61(2):325-334. doi: 10.1093/jrr/rrz103.
The aim of this study was to assess the impact of fractional dose and the number of arcs on interplay effects when volumetric modulated arc therapy (VMAT) is used to treat lung tumors with large respiratory motions. A three (fractional dose of 4, 7.5 or 12.5 Gy) by two (number of arcs, one or two) VMAT plan was created for 10 lung cancer cases. The median 3D tumor motion was 17.9 mm (range: 8.2-27.2 mm). Ten phase-specific subplans were generated by calculating the dose on each respiratory phase computed tomography (CT) scan using temporally assigned VMAT arcs. We performed temporal assignment of VMAT arcs using respiratory information obtained from infrared markers placed on the abdomens of the patients during CT simulations. Each phase-specific dose distribution was deformed onto exhale phase CT scans using contour-based deformable image registration, and a 4D plan was created by dose accumulation. The gross tumor volume dose of each 4D plan (4D GTV dose) was compared with the internal target volume dose of the original plan (3D ITV dose). The near-minimum 4D GTV dose (D99%) was higher than the near-minimum 3D internal target volume (ITV) dose, whereas the near-maximum 4D GTV dose (D1%) was lower than the near-maximum 3D ITV dose. However, the difference was negligible, and thus the 4D GTV dose corresponded well with the 3D ITV dose, regardless of the fractional dose and number of arcs. Therefore, interplay effects were negligible in VMAT-based stereotactic body radiation therapy for lung tumors with large respiratory motions.
本研究旨在评估当使用容积旋转调强放疗（VMAT）治疗具有大呼吸运动的肺部肿瘤时，分次剂量和弧数对相互作用效应的影响。为 10 例肺癌患者创建了三（分次剂量为 4、7.5 或 12.5 Gy）乘二（弧数，一个或两个）VMAT 计划。中位三维肿瘤运动为 17.9 mm（范围：8.2-27.2 mm）。通过计算每个呼吸相 CT 扫描上的剂量，使用按时间分配的 VMAT 弧生成了 10 个时相特异性子计划。我们使用在 CT 模拟期间放置在患者腹部的红外标记获得的呼吸信息来进行 VMAT 弧的时间分配。使用基于轮廓的变形图像配准将每个时相特异性剂量分布变形到呼气相 CT 扫描上，并通过剂量累加创建 4D 计划。每个 4D 计划的大体肿瘤体积剂量（4D GTV 剂量）与原始计划的内部靶区体积剂量（3D ITV 剂量）进行比较。近最小 4D GTV 剂量（D99%）高于近最小 3D ITV 剂量，而近最大 4D GTV 剂量（D1%）低于近最大 3D ITV 剂量。然而，差异可以忽略不计，因此 4D GTV 剂量与 3D ITV 剂量对应良好，与分次剂量和弧数无关。因此，在具有大呼吸运动的肺部肿瘤的立体定向体部放疗中，相互作用效应可以忽略不计。
