Background: Stereotactic body radiation therapy (SBRT) has proven effective in controlling spinal lesions with minimal toxicity, primarily due to its ability to limit spinal cord dose. Recent advances in MR-linac (MRL) technology offer superior spinal cord visualization and real-time gating, which can facilitate dose escalation in spinal tumor treatment while maintaining safety. Purpose: This study aimed to optimize motion management for spine SBRT on an MRL by analyzing patient-specific motion dynamics and evaluating the most effective registration structures. We hypothesized that baseline shifts (BLS) would improve delivery efficiency while maintaining spinal cord dose constraints. The goal was to establish displacement thresholds and assess the role of baseline shift correction adaptative planning in improving treatment delivery efficiency. Methods: Twelve patients underwent two MRI sessions on the MRL. The optimal registration structure was identified, and intrafraction motion was assessed to calculate delivery efficiency. Baseline shift (BLS) simulations were applied for five cases that showed significant motion and suboptimal delivery efficiency, and the dosimetric impact of the BLS was evaluated. The simulated BLS-based plan adaptation was implemented via a segment aperture morphing adapt-to-position workflow. Results: The most stable registration structure was the spinal canal plus three adjacent vertebrae. Cine imaging revealed average intrafraction motion (95th to 5th percentiles) of 0.8 ± 0.5 mm in the right-left (RL) direction, 0.9 ± 0.6 mm in the anterior–posterior (AP) direction, and 0.7 ± 0.5 mm in the SI direction. Simulated BLS improved delivery efficiency to >80% in all but one case, with a ±1 mm displacement threshold tolerance. While target coverage remained consistent after BLS simulation, the spinal cord dose increased by 7–60%, exceeding the 14 Gy constraint in three of the five simulated cases. Conclusions: Cine imaging and BLS can enhance delivery efficiency in spine SBRT but may increase spinal cord dose. These findings underscore the need for careful patient selection, advanced motion management, and patient-specific BLS protocols.
背景：立体定向放射治疗（SBRT）已被证明能有效控制脊柱病灶且毒性最小，这主要得益于其限制脊髓剂量的能力。磁共振直线加速器（MRL）技术的最新进展提供了卓越的脊髓可视化效果和实时门控功能，可在保证安全性的同时促进脊柱肿瘤治疗中的剂量提升。目的：本研究旨在通过分析患者特异性运动动态并评估最有效的配准结构，优化MRL上脊柱SBRT的运动管理。我们假设基线偏移（BLS）能在维持脊髓剂量限制的同时提高治疗实施效率。目标是建立位移阈值，并评估基线偏移校正自适应计划在提高治疗实施效率中的作用。方法：12名患者在MRL上接受了两次MRI扫描。确定了最佳配准结构，并评估了分次内运动以计算治疗实施效率。对五例显示显著运动和次优实施效率的病例应用了基线偏移（BLS）模拟，并评估了BLS的剂量学影响。通过分段孔径形变自适应定位工作流程实施了基于BLS的模拟计划调整。结果：最稳定的配准结构是椎管加上三个相邻椎体。动态成像显示分次内平均运动（第95百分位至第5百分位）在左右（RL）方向为0.8 ± 0.5毫米，前后（AP）方向为0.9 ± 0.6毫米，头脚（SI）方向为0.7 ± 0.5毫米。在±1毫米位移阈值容差下，模拟BLS将除一例外所有病例的治疗实施效率提高至>80%。虽然BLS模拟后靶区覆盖保持稳定，但脊髓剂量增加了7–60%，在五例模拟病例中有三例超过了14 Gy的限制。结论：动态成像和BLS可提高脊柱SBRT的治疗实施效率，但可能增加脊髓剂量。这些发现强调了需要仔细选择患者、采用先进的运动管理以及制定患者特异性的BLS方案。
肿瘤(癌症)患者之家