Radiation Medicine Research Center, Department of Radiation Oncology, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark.
Phys Med Biol. 2013 Apr 7;58(7):2349-61. doi: 10.1088/0031-9155/58/7/2349. Epub 2013 Mar 14.
This study investigated the dosimetric impact of uncompensated motion and motion compensation with dynamic multileaf collimator (DMLC) tracking for prostate intensity modulated arc therapy. Two treatment approaches were investigated; a conventional approach with a uniform radiation dose to the target volume and an intraprostatic lesion (IPL) boosted approach with an increased dose to a subvolume of the prostate. The impact on plan quality of optimizations with a leaf position constraint, which limited the distance between neighbouring adjacent MLC leaves, was also investigated. Deliveries were done with and without DMLC tracking on a linear acceleration with a high-resolution MLC. A cylindrical phantom containing two orthogonal diode arrays was used for dosimetry. A motion platform reproduced six patient-derived prostate motion traces, with the average displacement ranging from 1.0 to 8.9 mm during the first 75 s. A research DMLC tracking system was used for real-time motion compensation with optical monitoring for position input. The gamma index was used for evaluation, with measurements with a static phantom or the planned dose as reference, using 2% and 2 mm gamma criteria. The average pass rate with DMLC tracking was 99.9% (range 98.7-100%, measurement as reference), whereas the pass rate for untracked deliveries decreased distinctly as the average displacement increased, with an average pass rate of 61.3% (range 32.7-99.3%). Dose-volume histograms showed that DMLC tracking maintained the planned dose distributions in the presence of motion whereas traces with >3 mm average displacement caused clear plan degradation for untracked deliveries. The dose to the rectum and bladder had an evident dependence on the motion direction and amplitude for untracked deliveries, and the dose to the rectum was slightly increased for IPL boosted plans compared to conventional plans for anterior motion with large amplitude. In conclusion, optimization using a leaf position constraint had minimal dosimetric effect, DMLC tracking improved the target and normal tissue dose distributions compared to no tracking for target motion >3 mm, with the DMLC tracking distributions showing generally good agreement between the planned and delivered doses.
本研究调查了未补偿运动和使用动态多叶准直器 (DMLC) 跟踪进行前列腺强度调制弧形治疗的运动补偿的剂量学影响。研究了两种治疗方法；一种是对靶体积和前列腺内病变 (IPL) 进行均匀辐射剂量的常规方法，另一种是对前列腺的亚体积进行增加剂量的 IPL 增强方法。还研究了对优化施加叶位置限制的影响，该限制限制了相邻相邻多叶准直器叶片之间的距离。在具有高分辨率多叶准直器的线性加速下进行了无 DMLC 跟踪和有 DMLC 跟踪的输送。一个圆柱形体模包含两个正交二极管阵列，用于剂量测定。运动平台再现了六个源自患者的前列腺运动轨迹，在前 75 秒内的平均位移范围为 1.0 至 8.9 毫米。使用光学监测进行位置输入的研究型 DMLC 跟踪系统用于实时运动补偿。使用伽马指数进行评估，以静态体模或计划剂量作为参考，使用 2%和 2 毫米伽马标准。使用 DMLC 跟踪的平均通过率为 99.9%（范围为 98.7-100%，以测量作为参考），而无跟踪输送的通过率则随着平均位移的增加而明显下降，平均通过率为 61.3%（范围为 32.7-99.3%）。剂量体积直方图显示，DMLC 跟踪在存在运动的情况下维持了计划的剂量分布，而对于无跟踪输送，平均位移>3 毫米的轨迹导致计划明显恶化。对于无跟踪输送，直肠和膀胱的剂量明显取决于运动方向和幅度，对于大振幅前向运动的 IPL 增强计划，直肠的剂量与常规计划相比略有增加。总之，使用叶位置限制进行优化的剂量学影响最小，与无跟踪相比，DMLC 跟踪在目标运动>3 毫米时可改善靶区和正常组织的剂量分布，DMLC 跟踪分布通常与计划和输送剂量之间具有良好的一致性。
