Adamczyk Marta, Kruszyna-Mochalska Marta, Rucińska Anna, Piotrowski Tomasz
Department of Medical Physics, Greater Poland Cancer Centre, Poznań, Poland.
Department of Electroradiology, Poznań University of Medical Sciences, Poznań, Poland.
Rep Pract Oncol Radiother. 2020 Jul-Aug;25(4):684-691. doi: 10.1016/j.rpor.2020.06.003. Epub 2020 Jun 11.
Restricted studies comparing different dose rate parameters are available while ITV-based VMAT lung SBRT planning leads to perform the analysis of the most suitable parameters of the external beams used. The special emphasis was placed on the impact of dose rate on dose distribution variations in target volumes due to interplay effects.
Four VMAT plans were calculated for 15 lung tumours using 6 MV photon beam quality (flattening filter FF vs. flattening filter free FFF beams) and maximum dose rate of 600 MU/min, 1000 MU/min and 1400 MU/min. Three kinds of motion simulations were performed finally giving 180 plans with perturbed dose distributions.
6FFF-1400 MUs/min plans were characterized by the shortest beam on time (1.8 ± 0.2 min). Analysing the performed motion simulation results, the mean dose (Dmean) is not a sensitive parameter to related interplay effects. Looking for local maximum and local minimum doses, some discrepancies were found, but their significance was presented for individual patients, not for the whole cohort. The same was observed for other verified dose metrics.
Generally, the evaluation of VMAT robustness between FF and FFF concepts against interplay effect showed a negligible effect of simulated motion influence on tumour coverage among different photon beam quality parameters. Due to the lack of FFF beams, smaller radiotherapy centres are able to perform ITV-based VMAT lung SBRT treatment in a safe way. Radiotherapy department having FFF beams could perform safe, fast and efficient ITV-based VMAT lung SBRT without a concern about significance of interplay effects.
关于比较不同剂量率参数的研究有限，而基于 ITV 的 VMAT 肺部 SBRT 计划需要对所用外照射束的最合适参数进行分析。特别强调了剂量率对由于相互作用效应导致的靶区剂量分布变化的影响。
使用 6MV 光子束质量（有 flattening 滤波器 FF 与无 flattening 滤波器 FFF 束）以及 600MU/min、1000MU/min 和 1400MU/min 的最大剂量率，为 15 个肺部肿瘤计算了四个 VMAT 计划。最后进行了三种运动模拟，最终得到 180 个剂量分布受干扰的计划。
6FFF - 1400MU/min 计划的特点是束流开启时间最短（1.8±0.2 分钟）。分析所进行的运动模拟结果，平均剂量（Dmean）对相关相互作用效应不是一个敏感参数。在寻找局部最大和局部最小剂量时，发现了一些差异，但它们的意义是针对个体患者而言，而非整个队列。其他验证过的剂量指标也观察到了同样的情况。
总体而言，针对相互作用效应，FF 和 FFF 概念之间 VMAT 稳健性的评估表明，在不同光子束质量参数中，模拟运动对肿瘤覆盖的影响可忽略不计。由于缺乏 FFF 束，较小的放疗中心能够以安全的方式进行基于 ITV 的 VMAT 肺部 SBRT 治疗。拥有 FFF 束的放疗科可以进行安全、快速且高效的基于 ITV 的 VMAT 肺部 SBRT，而无需担心相互作用效应的显著性。
