质子调强放疗计划的鲁棒性优化方法研究

Research on robust optimization method of intensity-modulated proton therapy

目的提出改进最差场景算法,能够提升计划鲁棒性并且能平衡计划在标称场景下剂量分布质量与计划鲁棒性。方法对C形靶模型计划优化中,以标称场景优化为主,同时在每次迭代时计算每个体素在9种场景下的剂量值,取其与在标称场景下该体素剂量值的最大差值作为鲁棒性优化项添加入优化目标函数进行优化。结果在自主开发的鲁棒性优化计算模块验证,当权重因子probust=0.8时,相比常规优化,临床靶体积的ΔD95%由9.8Gy减小至7.6Gy。当probust由1减小到0时,ΔD95%由7.0Gy增大至9.8Gy,计划鲁棒性降低,而标称场景下CTV的D95%、Dmax和危及器官的D5%、Dmax减小,剂量分布质量得到提高。结论改进最差场景算法能够有效地提高计划对于射程和摆位不确定性的鲁棒性,并且该方法中probust可提供给计划制定者用于权衡治疗计划在标称场景的剂量分布质量和计划的鲁棒性。

Objective To propose a new robust optimization method,known as modified worst case method,was proposed,which can enable users to control the trade-off between nominal plan quality and plan robustness.Methods In each iteration of the plan optimization process,the dose value of each voxel in nine scenarios,which corresponded to a nominal scenario and eight perturbed scenarios with range or set-up uncertainties,were calculated and the maximum of deviations of each scenario voxel dose from that of the nominal scenario was included as an additive robust optimization term in the Objective function.A weighting factor probust was used to this robust optimization term to balance the nominal plan quality and plan robustness.Results The robust optimization methods were implemented and compared in an in-house developed robust optimization module.When probust=0.8,compared with conventional optimization,theΔD95%of CTV was reduced from 9.8 Gy to 7.6 Gy.When probust was reduced from 1 to 0,ΔD95%was increased from 7.0 Gy to 9.8 Gy,whereas the D95%and Dmax of CTV,and the D5%and Dmax of organs at risk(OAR)in the nominal scenario were reduced.Conclusions The proposed modified worst case method can effectively improve the robustness of the plan to the range and set-up uncertainties.Besides,the weighting factor probust in this method can be adopted to control the trade-off between nominal plan quality and plan robustness.