Department of Oncology, Aarhus University Hospital, Aarhus, Denmark. Radiation Application Research School, NSTRI, Tehran, Iran.
Phys Med Biol. 2018 Jul 16;63(14):145010. doi: 10.1088/1361-6560/aacdda.
The accuracy of stereotactic body radiotherapy (SBRT) in the liver is limited by tumor motion. Selection of the most suitable motion mitigation strategy requires good understanding of the geometric and dosimetric consequences. This study compares the geometric and dosimetric accuracy of actually delivered respiratory gated SBRT treatments for 15 patients with liver tumors with three simulated alternative motion adaptation strategies. The simulated alternatives are MLC tracking, baseline shift adaptation by inter-field couch corrections and no intrafraction motion adaptation. The patients received electromagnetic transponder-guided respiratory gated IMRT or conformal treatments in three fractions with a 3-4 mm gating window around the full exhale position. The CTV-PTV margin was 5 mm axially and 7-10 mm cranio-caudally. The CTV and PTV were covered with 95% and 67% of the prescribed mean CTV dose, respectively. The time-resolved target position error during treatments with the four investigated motion adaptation strategies was used to calculate motion margins and the motion-induced reduction in CTV D relative to the planned dose (ΔD ). The mean (range) number of couch corrections per treatment session to compensate for tumor drift was 2.8 (0-7) with gating, 1.4 (0-5) with baseline shift adaptation, and zero for the other strategies. The motion margins were 3.5 mm (left-right), 9.4 mm (cranio-caudal) and 3.9 mm (anterior-posterior) without intrafraction motion adaptation, approximately half of that with baseline shift adaptation, and 1-2 mm with MLC tracking and gating. With 7 mm CC margins the mean (range) of ΔD for the CTV was 8.1 (0.6-29.4)%-points (no intrafraction motion adaptation), 4.0 (0.4-13.3)%-points (baseline shift adaptation), 1.0 (0.3-2.2)%-points (MLC tracking) and 0.8 (0.1-1.8)%-points (gating). With 10 mm CC margins ΔD was instead 4.8 (0.3-14.8)%-points (no intrafraction motion adaptation) and 2.9 (0.2-9.8)%-points (baseline shift adaptation). In conclusion, baseline shift adaptation can mitigate gross dose deficits without the requirement of real-time motion adaptation. MLC tracking and gating, however, more effectively ensure high similarity between planned and delivered doses.
立体定向体部放射治疗（SBRT）在肝脏中的准确性受到肿瘤运动的限制。选择最合适的运动缓解策略需要很好地了解几何和剂量学的后果。本研究比较了 15 例肝脏肿瘤患者实际接受的呼吸门控 SBRT 治疗与三种模拟替代运动适应策略的几何和剂量学准确性。模拟的替代方案是 MLC 跟踪、通过场间床修正的基线偏移适应和无分次内运动适应。患者在 3-4mm 门控窗口内接受电磁转发器引导的呼吸门控调强放疗或适形治疗，共 3 个分次。CTV-PTV 边界在轴向为 5mm，颅尾向为 7-10mm。CTV 和 PTV 分别被 95%和 67%的计划CTV 平均剂量覆盖。使用四种研究的运动适应策略治疗期间的时间分辨靶区位置误差来计算运动边界和运动引起的 CTV D 相对于计划剂量的减少（ΔD）。补偿肿瘤漂移的每次治疗中床修正的平均（范围）次数为 2.8（0-7）次，有门控时为 1.4（0-5）次，其他策略为 0 次。无分次内运动适应时，运动边界为 3.5mm（左右）、9.4mm（颅尾向）和 3.9mm（前后），接近基线偏移适应时的一半，MLC 跟踪和门控时为 1-2mm。7mm CC 边界时，CTV 的平均（范围）ΔD为 8.1（0.6-29.4）%-点（无分次内运动适应）、4.0（0.4-13.3）%-点（基线偏移适应）、1.0（0.3-2.2）%-点（MLC 跟踪）和 0.8（0.1-1.8）%-点（门控）。当使用 10mm CC 边界时，ΔD 为 4.8（0.3-14.8）%-点（无分次内运动适应）和 2.9（0.2-9.8）%-点（基线偏移适应）。总之，基线偏移适应可以在不需要实时运动适应的情况下减轻总剂量不足。然而，MLC 跟踪和门控更有效地确保计划和给予剂量之间的高度相似性。
