Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, SM2 5PT, UK.
Med Phys. 2019 Dec;46(12):5421-5433. doi: 10.1002/mp.13848. Epub 2019 Oct 22.
The use of dynamic arcs for delivery of stereotactic body radiation therapy (SBRT) on Cyberknife is investigated, with a view to improving treatment times. This study investigates the required modeling of robot and multileaf collimator (MLC) motion between control points in the trajectory and then uses this to develop an optimization method for treatment planning of a dynamic arc with Cyberknife. The resulting plans are compared in terms of dose-volume histograms and estimated treatment times with those produced by a conventional beam arrangement.
Five SBRT patient cases (prostate A - conventional, prostate B - brachytherapy-type, lung, liver, and partial left breast) were retrospectively studied. A suitable arc trajectory with control points spaced at 5° was proposed and treatment plans were produced for typical clinical protocols. The optimization consisted of a fluence optimization, segmentation, and direct aperture optimization using a gradient descent method. Dose delivered by the moving MLC was either taken to be the dose delivered discretely at the control points or modeled using effective fluence delivered between control points. The accuracy of calculated dose was assessed by recalculating after optimization using five interpolated beams and 100 interpolated apertures between each optimization control point. The resulting plans were compared using dose-volume histograms and estimated treatment times with those for a conventional Cyberknife beam arrangement.
If optimization is performed based on discrete doses delivered at the arc control points, large differences of up to 40% of the prescribed dose are seen when recalculating with interpolation. When the effective fluence between control points is taken into account during optimization, dosimetric differences are <2% for most structures when the plans are recalculated using intermediate nodes, but there are differences of up to 15% peripherally. Treatment plan quality is comparable between the arc trajectory and conventional body path. All plans meet the relevant clinical goals, with the exception of specific structures which overlap with the planning target volume. Median estimated treatment time is 355 s (range 235-672 s) for arc delivery and 675 s (range 554-1025 s) for conventional delivery.
The method of using effective fluence to model MLC motion between control points is sufficiently accurate to provide for accurate inverse planning of dynamic arcs with Cyberknife. The proposed arcing method produces treatment plans with comparable quality to the body path, with reduced estimated treatment delivery time.
研究在 Cyberknife 上使用动态弧进行立体定向体放射治疗（SBRT），以缩短治疗时间。本研究探讨了在轨迹控制点之间对机器人和多叶准直器（MLC）运动进行建模的必要性，然后利用这一模型为 Cyberknife 的动态弧治疗计划开发了一种优化方法。通过剂量-体积直方图和估计的治疗时间来比较结果计划与传统射束排列产生的计划。
回顾性研究了 5 例 SBRT 患者（前列腺 A-传统，前列腺 B-近距离放射治疗型，肺，肝和左半乳）。提出了一个合适的具有 5°间隔的弧形轨迹，并为典型的临床方案生成了治疗计划。优化由通量优化、分段和使用梯度下降法的直接孔径优化组成。移动 MLC 传递的剂量要么被视为在控制点离散传递的剂量，要么通过在控制点之间传递的有效通量进行建模。通过在优化后使用五个插值射束和每个优化控制点之间的 100 个插值孔径重新计算来评估计算剂量的准确性。通过剂量-体积直方图和与传统 Cyberknife 射束排列的估计治疗时间来比较结果计划。
如果基于在弧形控制点处传递的离散剂量进行优化，则在使用插值重新计算时会看到高达 40%的处方剂量的较大差异。在优化过程中考虑到控制点之间的有效通量时，当使用中间节点重新计算计划时，大多数结构的剂量差异<2%，但在周围区域会有高达 15%的差异。弧形轨迹和传统体路径的治疗计划质量相当。除了与计划靶区重叠的特定结构外，所有计划都符合相关的临床目标。估计的中位治疗时间为弧形传递 355 s（范围 235-672 s），传统传递 675 s（范围 554-1025 s）。
使用有效通量在控制点之间对 MLC 运动进行建模的方法足够准确，可以为 Cyberknife 的动态弧形进行精确的逆向计划。所提出的弧形方法产生的治疗计划与体路径的质量相当，估计的治疗输送时间缩短。
