Department of Oncology, KU Leuven, Belgium; Department of Radiation Oncology, University Hospitals Leuven, Belgium.
Department of Medical Physics, Aarhus University Hospital, Denmark.
Radiother Oncol. 2021 Mar;156:10-18. doi: 10.1016/j.radonc.2020.11.031. Epub 2020 Nov 29.
Both gating and tracking can mitigate the deteriorating dosimetric impact of intrafraction translation during prostate stereotactic body radiotherapy (SBRT). However, their ability to manage intrafraction rotation has not yet been thoroughly investigated. The dosimetric accuracy of gating, MLC tracking and couch tracking to manage intrafraction prostate rotation was investigated.
Treatment plans for end-to-end tests of prostate SBRT with focal boosting were generated for a dynamic anthropomorphic pelvis phantom. The phantom applied internal lateral rotation (up to 25°) and coupled vertical and longitudinal translation of a radiochromic film stack that was used for dose measurements. Dose was delivered for each plan while the phantom applied motion according to three typical prostate motion traces without compensation (i), with gating (ii), with MLC tracking (iii) or with couch tracking (iv). Measured doses for the four motion compensation strategies were compared with the planned dose in terms of γ-index analysis, target coverage and organs at risk (OAR) sparing.
Intrafraction rotation reduced the 3%(global)/2mm γ-index passing rate (γPR) for the prostate target volume by median (range) -33.2% (-68.6%, -4.1%) when no motion compensation was applied. The use of motion compensation improved the γPR by 13.2% (-0.4%, 32.9%) for gating, by 6.0% (-0.8%, 27.7%) for MLC tracking and by 11.1% (1.2%, 22.9%) for couch tracking. The three compensation techniques improved the target coverage in most cases. Gating showed better OAR sparing than MLC tracking or couch tracking.
Compensation of intrafraction prostate rotation with gating, MLC tracking and couch tracking was investigated experimentally for the first time. All three techniques improved the dosimetric accuracy, but residual motion-related dose errors remained due to the lack of rotation correction.
门控和跟踪都可以减轻前列腺立体定向体部放射治疗（SBRT）过程中分次内平移导致的剂量学恶化。然而，它们管理分次内旋转的能力尚未得到充分研究。本研究旨在研究门控、MLC 跟踪和床跟踪管理分次内前列腺旋转的剂量学准确性。
针对端到端前列腺 SBRT 加量照射的测试，为动态人体骨盆模型生成了治疗计划。该模型施加了内部侧向旋转（最高 25°）以及放射性色膜叠层的垂直和纵向耦合平移，用于剂量测量。在没有补偿的情况下，根据三个典型的前列腺运动轨迹（无补偿），通过门控（ii）、MLC 跟踪（iii）或床跟踪（iv）为每个计划输送剂量，同时模型施加运动。从γ指数分析、靶区覆盖和危及器官（OAR）保护等方面，比较了这四种运动补偿策略的测量剂量与计划剂量的差异。
分次内旋转降低了前列腺靶区体积的 3%（总体）/2mm γ 指数通过率（γPR），中位数（范围）为-33.2%（-68.6%，-4.1%），无运动补偿时。使用运动补偿，门控可使 γPR 提高 13.2%（0.4%，32.9%），MLC 跟踪提高 6.0%（0.8%，27.7%），床跟踪提高 11.1%（1.2%，22.9%）。三种补偿技术在大多数情况下都改善了靶区覆盖。门控在 OAR 保护方面优于 MLC 跟踪或床跟踪。
首次对门控、MLC 跟踪和床跟踪补偿分次内前列腺旋转进行了实验研究。这三种技术都提高了剂量学准确性，但由于缺乏旋转校正，仍然存在与运动相关的剂量误差。
