Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, 1275 York Ave, New York, NY 10021, USA.
Phys Med Biol. 2013 Nov 7;58(21):7803-13. doi: 10.1088/0031-9155/58/21/7803. Epub 2013 Oct 21.
To develop an optimization algorithm for volumetric modulated arc therapy which incorporates an electromagnetic tracking (EMT) guided gating strategy and is robust to residual intra-fractional motion uncertainties. In a computer simulation, intra-fractional motion traces from prior treatments with EMT were converted to a probability distribution function (PDF), truncated using a patient specific action volume that encloses allowed deviations from the planned position, and renormalized to yield a new PDF with EMT-gated interventions. In lieu of a conventional planning target volume (PTV), multiple instances of clinical target volume (CTV) and organs at risk (OARs) were replicated and displaced to extreme positions inside the action volume representing possible delivery scenarios. When optimizing the volumetric modulated arc therapy plan, doses to the CTV and OARs were calculated as a sum of doses to the replicas weighted by the PDF to account for motion. A treatment plan meeting the clinical constraints was produced and compared to the counterpart conventional margin (PTV) plan. EMT traces from a separate testing database served to simulate motion during gated delivery. Dosimetric end points extracted from dose accumulations for each motion trace were utilized to evaluate potential clinical benefit. Five prostate cases from a hypofractionated protocol (42.5 Gy in 5 fractions) were retrospectively investigated. The patient specific gating window resulted in tight anterior and inferior action levels (~1 mm) to protect rectal wall and bladder wall, and resulted in an average of four beam interruptions per fraction in the simulation. The robust-optimized plans achieved the same average CTV D95 coverage of 40.5 Gy as the PTV-optimized plans, but with reduced patient-averaged rectum wall D1cc by 2.2 Gy (range 0.7 to 4.7 Gy) and bladder wall mean dose by 2.9 Gy (range 2.0 to 3.4 Gy). Integration of an intra-fractional motion management strategy into the robust optimization process is feasible and may yield improved OAR sparing compared to the standard margin approach.
开发一种容积调强弧形治疗的优化算法，该算法结合了电磁跟踪（EMT）引导的门控策略，并且对残余的分次内运动不确定性具有鲁棒性。在计算机模拟中，将来自先前 EMT 治疗的分次内运动轨迹转换为概率分布函数（PDF），使用包含计划位置允许偏差的患者特定作用体积截断 PDF，并重新归一化以生成具有 EMT 门控干预的新 PDF。代替传统的计划靶区（PTV），多个临床靶区（CTV）和危及器官（OAR）的实例被复制并移动到作用体积内的极端位置，代表可能的传递场景。在优化容积调强弧形治疗计划时，将 CTV 和 OAR 的剂量计算为副本的剂量之和，副本的权重由 PDF 给出，以考虑运动。生成满足临床约束的治疗计划，并与常规边缘（PTV）计划进行比较。来自单独测试数据库的 EMT 轨迹用于模拟门控传递期间的运动。从每个运动轨迹的剂量累积中提取剂量学终点，以评估潜在的临床获益。从一个低分割方案（5 次分割 42.5 Gy）回顾性研究了 5 例前列腺病例。患者特定的门控窗口导致前壁和下壁的作用水平非常接近（~1mm），以保护直肠壁和膀胱壁，并且在模拟中，每个分割平均有 4 次光束中断。稳健优化计划达到了与 PTV 优化计划相同的平均 CTV D95 覆盖 40.5 Gy，但患者平均直肠壁 D1cc 降低了 2.2 Gy（范围 0.7 至 4.7 Gy），膀胱壁平均剂量降低了 2.9 Gy（范围 2.0 至 3.4 Gy）。将分次内运动管理策略集成到稳健优化过程中是可行的，与标准边缘方法相比，可能会改善 OAR 保护。
