Department of Physics and Atmospheric Science, Dalhousie University, Canada.
Department of Radiation Oncology, Dalhousie University, Canada.
Biomed Phys Eng Express. 2022 Jul 7;8(5). doi: 10.1088/2057-1976/ac7c92.
C-arm linac-based radiotherapy has seen a recent interest in 4methods of delivery using simultaneous rotations of couch and gantry to reduce doses to organs-at-risk (OARs) and increase dose compactness. While many methods use heuristics to generate trajectories that avoid OARs, combined with arbitrary trajectory restrictions to prevent oversampling, a quantity has not yet been developed to succinctly compare sampling of the 4space for candidate trajectories as a surrogate for dosimetric compactness.Evenly spaced sampling points were distributed across a 4sphere centred on isocentre. A metric, mean arc distance (MAD), was defined that quantifies the average arc distance between all sampling points and their nearest field in a radiotherapy trajectory. The relationship between isodose volume and MAD was examined in 2,047 plans: 900 unique trajectories of fixed port DCA plans, 900 unique trajectories of contiguous field DCA plans, 192 VMAT plans (eight volumes in four locations, each with six trajectories) in matRad with 5 VMAT plans repeated for validation in a clinical planning system, and 10 clinical VMAT cases replanned with five trajectories in a clinical treatment planning system.All isodose volumes greater than 10% of the prescription dose decreased with decreasing MAD in all comparisons. In the range of 10% to 100% of the prescription dose, the rate of isodose volume decrease was exponential as a function of MAD in all comparisons. Reduction of absolute isodose volume is seen with increased 4sampling, with larger target volumes exhibiting larger absolute reductions. Very low isodoses (0% to 10% of prescription) increased with decreasing MAD.MAD is a 4sampling quantity useful in quantifying the decrease of isodose volume, relevant for sparing normal tissues. By quantifying this feature, candidate dynamic trajectories can be efficiently compared for 4sampling. This quantity is explored here for single target cranial radiotherapy but may have applications to other radiotherapy treatment sites.
C 臂直线加速器放射治疗最近对 4 种使用同时旋转治疗床和机架的方法产生了兴趣，这些方法旨在降低危及器官（OAR）的剂量并提高剂量紧凑性。虽然许多方法使用启发式方法生成避开 OAR 的轨迹，并结合任意轨迹限制来防止过度采样，但尚未开发出一种数量来简洁地比较候选轨迹在 4 空间中的采样情况，作为剂量紧凑性的替代指标。均匀间隔的采样点分布在以等中心为中心的 4 球面上。定义了一个度量标准，即平均弧距（MAD），它量化了放射治疗轨迹中所有采样点与其最近射野之间的平均弧距。在 2047 个计划中检查了等剂量体积与 MAD 的关系：900 个固定端口 DCA 计划的独特轨迹，900 个连续射野 DCA 计划的独特轨迹，192 个 VMAT 计划（在 matRad 中有四个位置的 8 个体积，每个体积有 6 个轨迹），其中 5 个 VMAT 计划在临床计划系统中重复验证，以及 10 个临床 VMAT 病例在临床治疗计划系统中使用 5 个轨迹重新计划。在所有比较中，所有等剂量体积大于处方剂量的 10%都随着 MAD 的降低而降低。在处方剂量的 10%到 100%范围内，所有比较中，等剂量体积的减少率都是 MAD 的指数函数。随着 4 采样的增加，绝对等剂量体积会减少，靶区体积越大，绝对减少量越大。非常低的等剂量（处方剂量的 0%到 10%）随着 MAD 的降低而增加。MAD 是一个 4 采样数量，可用于量化等剂量体积的减少，这对于保护正常组织很重要。通过量化这一特征，可以有效地比较候选动态轨迹的 4 采样。本文探讨了该数量在单靶颅放疗中的应用，但可能适用于其他放疗治疗部位。
