Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI, USA.
Med Phys. 2013 Jan;40(1):011704. doi: 10.1118/1.4769119.
To evaluate the feasibility of planning and delivering pulsed low dose radiotherapy (PLRT) using volumetric modulated arc therapy (VMAT) on Elektalinacs.
Ten patients previously treated for glioblastomamultiforme (GBM) were replanned using PLRT VMAT to deliver ten 0.2 Gy pulses separated by 3 min intervals with an effective dose rate of 0.067 Gy∕min. VMAT parameters such as leaf speed and arc length were investigated to deliver 2 Gy∕fraction to a total of 60 Gy to the target volume in ten subfractions or pulses. Plan quality was assessed using conformity and homogeneity indices. Absolute dose distribution for individual pulses was measured using ArcCHECK diode array. Individual pulses were analyzed for reproducibility and stability using machine log files. Machine characteristics at low monitor units and low dose rate were also investigated.
An optimal arc length of 140°-160° and a leaf speed of 0.18-0.25 cm∕° were sufficient to provide equivalent plan coverage and stable delivery. The average time and dose rate required to deliver a single 0.2 Gy pulse was 39.5 ± 2.3 s and 49 ± 32.3 cGy∕min. Average reductions in MUs for the VMAT PLRT plan compared to IMRT for PTV was 16% (Range: -5.5%-36.1%) and 10.9% (Range: -18.4%-32.3%) for the initial and boost plan. A significant improvement was seen in maximum doses to all sensitive structures when planned with VMAT PLRT. The average absolute dose gamma passing rate for the 10 pulses combined and 2 Gy plan were 91.6 ± 2.5% and 97.3 ± 1.2%, respectively. Cumulative monitor units, dose rate, gantry angles, and leaf positions evaluated using machine log files were within 2% for all pulses.
Elekta linacs are capable of delivering reproducible and stable PLRT plans. A prospective clinical study employing PLRT is currently in development.
评估在 Elekta 直线加速器上使用容积旋转调强弧形治疗（VMAT）规划和实施脉冲低剂量放疗（PLRT）的可行性。
对 10 例先前接受多形性胶质母细胞瘤（GBM）治疗的患者进行再计划，采用 PLRT VMAT 技术，每 3 分钟间隔给予 10 个 0.2Gy 脉冲，有效剂量率为 0.067Gy/min。研究了叶片速度和弧形长度等 VMAT 参数，以在 10 个子分次或脉冲中将 2Gy/分次的总剂量 60Gy 传递至靶区。使用适形性和均匀性指数评估计划质量。使用 ArcCHECK 二极管阵列测量各个脉冲的绝对剂量分布。使用机器日志文件分析各个脉冲的可重复性和稳定性。还研究了低剂量率和低剂量率下的机器特性。
140°-160°的最佳弧形长度和 0.18-0.25cm/°的叶片速度足以提供等效的计划覆盖范围和稳定的传递。单次 0.2Gy 脉冲的平均时间和剂量率分别为 39.5±2.3s 和 49±32.3cGy/min。与初始和增强计划的调强放疗相比，VMAT PLRT 计划的平均 MU 降低了 16%（范围：-5.5%-36.1%）和 10.9%（范围：-18.4%-32.3%）。当使用 VMAT PLRT 进行计划时，所有敏感结构的最大剂量均显著改善。10 个脉冲的累积和 2Gy 计划的平均绝对剂量伽玛通过率分别为 91.6±2.5%和 97.3±1.2%。使用机器日志文件评估的累积监视器单位、剂量率、龙门角度和叶片位置在所有脉冲中均在 2%以内。
Elekta 直线加速器能够提供可重复和稳定的 PLRT 计划。目前正在开展采用 PLRT 的前瞻性临床研究。
