Department of Radiation Oncology, "G. D'Annunzio" University, "SS. Annunziata" Hospital, Chieti, Italy.
Medical Physics Department, Veneto Institute of Oncology IOV-IRCCS, via Gattamelata 64, Padova, Italy.
Phys Med. 2021 Aug;88:98-103. doi: 10.1016/j.ejmp.2021.06.008. Epub 2021 Jun 30.
The influence of basic plan parameters such as slice thickness, grid resolution, algorithm type and field size on calculated small field output factors (OFs) was evaluated in a multicentric study.
Three computational homogeneous water phantoms with slice thicknesses (ST) 1, 2 and 3 mm were shared among twenty-one centers to calculate OFs for 1x1, 2x2 and 3x3 cm field sizes (FSs) (normalized to 10x10 cm FS), with their own treatment planning system (TPS) and the energy clinically used for stereotactic body radiation therapy delivery. OFs were calculated for each combination of grid resolution (GR) (1, 2 and 3 mm) and ST and finally compared with the OFs measured for the TPS commissioning. A multivariate analysis was performed to test the effect of basic plan parameters on calculated OFs.
A total of 509 data points were collected. Calculated OFs are slightly higher than measured ones. The multivariate analysis showed that Center, GR, algorithm type, and FS are predictive variables of the difference between calculated and measured OFs (p < 0.001). As FS decreases, the spread in the difference between calculated and measured OFs became larger when increasing the GR. Monte Carlo and Analytical Anisotropic Algorithms, presented a dependence on GR (p < 0.01), while Collapsed Cone Convolution and Acuros did not. The effect of the ST was found to be negligible.
Modern TPSs slightly overestimate the calculated small field OFs compared with measured ones. Grid resolution, algorithm, center number and field size influence the calculation of small field OFs.
在一项多中心研究中，评估了诸如切片厚度、网格分辨率、算法类型和射野大小等基本计划参数对计算小射野输出因子（OFs）的影响。
三个具有 1、2 和 3 毫米切片厚度的计算均匀水体模在二十一个中心之间共享，以计算 1x1、2x2 和 3x3 厘米射野大小（归一化为 10x10 厘米射野）的 OFs，使用各自的治疗计划系统（TPS）和临床用于立体定向体放射治疗的能量。为每个网格分辨率（GR）（1、2 和 3 毫米）和 ST 组合计算 OFs，最后与 TPS 委托测量的 OFs进行比较。进行了多变量分析以检验基本计划参数对计算 OFs 的影响。
共收集了 509 个数据点。计算的 OFs 略高于测量值。多变量分析表明，中心、GR、算法类型和 FS 是计算和测量 OFs 之间差异的预测变量（p<0.001）。随着 FS 的减小，当 GR 增加时，计算和测量 OFs 之间的差异分布变得更大。Monte Carlo 和 Analytical Anisotropic Algorithms 呈现出对 GR 的依赖性（p<0.01），而 Collapsed Cone Convolution 和 Acuros 则没有。ST 的影响被发现可以忽略不计。
与测量值相比，现代 TPS 略微高估了计算的小射野 OFs。网格分辨率、算法、中心数量和射野大小会影响小射野 OFs 的计算。
