几何不确定性鲁棒优化在肝癌立体定向放疗中的应用

目的：分析基于几何不确定性的鲁棒优化计划对肝癌立体定向放疗(SBRT)剂量分布的影响。方法：选取12例肝癌SBRT患者，对每例制作3个调强计划：①基于PTV(ITV-PTV 5 mm)的常规优化(PTV-Based Plan)；②基于ITV非均匀几何不确定性(本中心计算的不确定性值：进出方向7 mm，左右和前后方向4 mm)的鲁棒优化(Robust Plan_actual)；③基于ITV均匀5 mm几何不确定性的鲁棒优化(Robust Plan_{5 mm})。所有计划都以95%的PTV满足处方剂量作为目标，以等中心均匀偏移4、5、7 mm计算扰动剂量评估鲁棒性。结果：计划①②③的均匀性指数(HI)分别为0.083±0.027、0.099±0.035、0.096±0.026，不具有统计学意义；计划①②③的适形性指数(CI)分别为0.98±0.02、1.02±0.05、1.00±0.04，计划②③相对于计划①的CI具有统计学意义。计划③的正常肝组织平均受量和V₂₅₀₀相对于计划①②分别下降了4.1%、2.5%和5.4%、3.0%，...

Application of geometric uncertainty-based robust optimization in stereotactic body radiotherapy for liver cancer

Objective To analyze the effects of robust optimization plan based on geometric uncertainty on the dose distribution of stereotactic body radiotherapy(SBRT)for liver cancer.Methods Twelve patients treated by SBRT for liver cancer were enrolled in the study.For each case,3 different kinds of plans were designed by different optimization methods,including①conventional optimization(PTV-Based Plan)based on PTV(ITV-PTV _(5 mm)),②robust optimization(Robust Planactual)based on non-uniform geometric uncertainty for ITV(the uncertainties calculated by our center were 7 mm in superior-inferior direction,4 mm in medial-lateral and anterior-posterior directions),③robust optimization(Robust Plan5 mm)based on uniform geometric uncertainty of 5 mm for ITV.All plans were based on the target that 95%ITV met the prescribed dose,and the perturbation dose was calculated with uniform uncertainties of 4,5,7 mm from the isocenter to evaluate the robustness.Results The homogeneity index of plans①②③was 0.083±0.027,0.099±0.035 and 0.096±0.026,respectively,without statistical significance;and the conformity index of plans②③was 1.02±0.05,1.00±0.04,significantly different from that of plan①which was 0.98±0.02.Compared with those in plans①②,the average dose to normal liver tissues in plan③was decreased by 4.1%and 2.5%(P=0.034,P=0.021),and V2500was decreased by 5.4%and 3.0%(P=0.004,P=0.004),respectively.The average dose to normal liver tissue and V₂₅₀₀in plan②were not statistically different from those in plan①(P=0.308 and P=0.182),but decreased by 1.6%and 2.5%.For robustness,the differences in dose-volume histogram bandwidth(DVHBW)of 5 mm-D_99%,5 mm-D_98%,5 mm-D_95%in plans②③were smaller than those in plan①.With the increase of setup uncertainty,the difference in DVHBW became greater.Conclusion In liver SBRT,robust optimization can optimize target dose distribution.Even if the setup uncertainty increases,it can still ensure the dose coverage of ITV,without increasing the irradiation dose to normal tissues.