Department of Engineering and Applied Physics, University of Science and Technology of China, Hefei, Anhui, China.
Department of Radiation Oncology, the First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui, China.
J Appl Clin Med Phys. 2023 Oct;24(10):e14078. doi: 10.1002/acm2.14078. Epub 2023 Jun 19.
To investigate the dosimetry effects of different gating strategies in cine magnetic resonance imaging (MRI)-guided breath-hold pancreatic cancer radiotherapy.
Two cine MRI-based gating strategies were investigated： a tumor contour-based gating strategy at a gating threshold of 0-5% and a tumor displacement-based gating strategy at a gating threshold of 3-5 mm. The cine MRI videos were obtained from 17 pancreatic cancer patients who received MRI-guided radiation therapy. We calculated the tumor displacement in each cine MR frame that satisfied the gating threshold and obtained the proportion of frames with different displacements. We generated IMRT and VMAT plans using a 33 Gy prescription, and motion plans were generated by adding up all isocenter-shift plans corresponding to different tumor displacements. The dose parameters of GTV, PTV, and organs at risk (OAR) were compared between the original and motion plans.
In both gating strategies, the difference was significant in PTV coverage but not in GTV coverage between the original and motion plans. OAR dose parameters deteriorate with increasing gating threshold. The beam duty cycle increased from 19.5±14.3% (median 18.0%) to 60.8±15.6% (61.1%) for gating thresholds from 0% to 5% in tumor contour-based gating and from 51.7±11.5% (49.7%) to 67.3±12.4% (67.1%) for gating thresholds from 3 to 5 mm in tumor displacement-based gating.
In tumor contour-based gating strategy, the dose delivery accuracy deteriorates while the dose delivery efficiency improves with increasing gating thresholds. To ensure treatment efficiency, the gating threshold might be no less than 3%. A threshold up to 5% may be acceptable in terms of the GTV coverage. The displacement-based gating strategy may serve as a potential alternative to the tumor contour based gating strategy, in which the gating threshold of approximately 4 mm might be a good choice for reasonably balancing the dose delivery accuracy and efficiency.
研究不同门控策略在磁共振引导屏气胰腺癌放疗中的剂量学效应。
研究了两种基于电影磁共振成像（MRI）的门控策略：门控阈值为 0-5%的肿瘤轮廓门控策略和门控阈值为 3-5mm 的肿瘤位移门控策略。从 17 名接受 MRI 引导放疗的胰腺癌患者中获得电影 MRI 视频。我们计算了满足门控阈值的每个电影磁共振帧中的肿瘤位移，并获得了不同位移帧的比例。我们使用 33Gy 处方生成了调强放疗（IMRT）和容积旋转调强放疗（VMAT）计划，并通过添加与不同肿瘤位移相对应的所有等中心点移位计划生成运动计划。比较了原始和运动计划中 GTV、PTV 和危及器官（OAR）的剂量参数。
在两种门控策略中，原始和运动计划之间的 PTV 覆盖差异显著，但 GTV 覆盖差异不显著。OAR 剂量参数随门控阈值的增加而恶化。对于肿瘤轮廓门控，门控阈值从 0%增加到 5%，束流占空比从 19.5±14.3%（中位数 18.0%）增加到 60.8±15.6%（61.1%）；对于肿瘤位移门控，门控阈值从 3 增加到 5mm，束流占空比从 51.7±11.5%（49.7%）增加到 67.3±12.4%（67.1%）。
在肿瘤轮廓门控策略中，随着门控阈值的增加，剂量传递精度恶化，而剂量传递效率提高。为了确保治疗效率，门控阈值可能不低于 3%。在 GTV 覆盖方面，门控阈值高达 5%可能是可以接受的。基于位移的门控策略可能是基于肿瘤轮廓的门控策略的一种潜在替代方案，其中门控阈值约为 4mm 可能是合理平衡剂量传递精度和效率的良好选择。
