Impact of fluence smoothing on the dosimetry of cervical cancer radiotherapy

Abstract

Objective To explore the dosimetric differences of radiotherapy plan for cervical cancer with 4 different fluence smoothing (FS) parameters using Monaco treatment planning system (Monaco TPS). Methods Fifteen patients with I B2 stage cervical cancer in our hospital were enrolled in this study. And a 2 Volumetric Modulated Arc Therapy (VMAT) plan for each patient were completed by Monaco 5.11 TPS according to the X-Ray Voxel Monte Carlo (XVMC) method. For each plan was optimized by FS function, with the level of Off, Low, Medium and High. To compare the difference of plan optimization time, conformity index ( CI), Homogeneity index ( HI), D mean, D min, D 2% of PTV, dose to the organ at risk (OAR), the number of Segments# and MU#, estimated total delivery time (ETDT), quantum Efficiency (QE) of the plans, the formation of Segments# with the same angle and verification of inserting 729 two-dimensional matrix into PTW octavius 4D module of different FS function levels, with the precondition of the Prescription isodose curve covering 95% of the target area. The data was analysed by multivariate factor analysis with the application of SPSS, and P < 0.05 was considered as statistically significant. And the Planned revenue score of different FS levels was also calculated. Results Except for the D min of PTV (the lowest value is (32.09 ± 0.26) Gy for the Off group, and the highest value is (35.98 ± 0.42) Gy for the High group), V 40 of the rectum (the lowest value in the Medium group is 55.88% ± 2.02%, and the highest value in the High group was 61.90% ± 2.98%) and bladder (the lowest value was 45.01% ± 2.08% in the Medium group, and the highest value is 50.45% ± 1.98% in the High group), the V 20 (the lowest value High group was 49.05% ± 1.98%, the highest value Off group was 56.52 ± 1.75%) of femoral head ( P < 0.05), there was no significant difference of the dose assessment results for PTV and OARs in 4 different FS function levels. In the High level, the ETDT, QE and MU# were showed better than other groups evidently, however, the number of Segments# showed no significant difference. The plan validation results was increased with the improvement of FS function level, and the level of High was considered to be the optimal. To compare the score of overall benefits of the plan, the level of Medium (−17.18 ± 0.05) got the highest score, and the Low group (−17.58 ± 0.05) and the High group (−17.42 ± 0.06) have similar scores, and Off group (−18.81 ± 0.08) has the lowest score. Conclusion Different FS levels of the Monaco 5.11 TPS can optimize the radiotherapy plan for cervical cancer, but the level of Medium is considered to be the most applicable. 摘要： 目的 研宄 Monaco 计划系统 (Monaco Treatment planning system, Monaco TPS) 应用不同通量平滑度 (Fluence smoothing, FS) 的情况下, 对宫颈癌放射治疗的剂量学影响。 方法 选取 I B2 期宫颈癌患者 15 例进行入组实验, 使用 瑞典医科达公司 Monaco 5.11TPS 的 X 射线体素蒙特卡洛 (X-ray voxel Monte Carlo, XVMC) 算法, 对每例入组病例分 别进行由 Off〜High 4 个不同等级通量优化平滑作用下, 2 个全弧的空间容积调强 (Volumetric modulated arc therapy, VMAT) 计划设计。在处方剂量均覆盖计划|E区 (Planning target volume, PTV) 95% 体积的情况下, 比对不同等级通量 平滑度作用下的计划优化时间, PTV 的适形指数 (Conformity index, CI) 和均句性指数 (Homogeneity index, HI) 以及平 均剂量 D mean、最小剂量 D min、最大剂量 D 2%, 危机器官 (Organ at risk, OAR) 受量, 计划应用子野数量 (Segments#), 计划 实施跳数 (MU#), 计划优化时长 (Estimated total delivery time, ETDT), 光子利用率 (Quantum efficiency, QE) 以及相同 角度子野构成和在 PTW Octavius 4D 模体内插 729 二维矩阵方式下的验证结果差异; 使用 SPSS 进行方差分析, P < 0.05 具有统计学意义;并计算不同 FS 等级设定下计划收益得分。 结果 在不同 FS 功能等级作用下的 4 个实验组的 PTV 和 OARs 剂量评估结果中, 除 PTV 的 D min [最低值为 Off 组 (32.09 ± 0.26) Gy, 最高值为 High 组 (35.98 ± 0.42)Gy]、直肠 (最低值 Medium 组 55.88% ± 2.02%, 最高值 High 组 61.90% ± 2.98%) 和膀胱 (最低值为 Medium 组 45.01 ± 2.08%, 最高值 High 组 50.45 ± 1.98%) 的 V 40、股骨头 (最低值 High 组 49.05% ± 1.98%, 最高值 Off 组 56.52% ± 1.75%) 的 V 20, 差异均有统计学意义 ( P < 0.05); 计划剂量计算时间、光子利用率和计划应用空气跳数上 High 组的结果 明显优于其他 FS 等级, 而计划子野应用数量上 4 个 FS 功能等级上无明显差异;计划验证结果对比中伴随 FS 功能等 级的提高而增加, High 组验证结果最优; 计划整体收益得分中 Medium 组 (−17.18 ± 0.05) 得分最高, Low 组 (−17.58 ± 0.05) 和 High 组 (−17.42 ± 0.06) 得分接近, Off 组 (−18.81 ± 0.08) 为最低。 结论 应用 Monaco 5.11 TPS 进行优化宫颈 癌放射治疗计划时, 不同 FS 功能等级下的计划结果均符合临床要求, 但综合评估结果应用 Medium 是最为适用的。