基于模板库实施VMAT计划自动优化初步研究

A preliminary study of template library-based auto-planning of volume modulated arc therapy

目的 研究基于优化条件模板库实施容积调强弧形治疗（VMAT）治疗计划自动优化的可行性.方法 回顾选择Eclipse计划系统VMAT计划直肠癌术后患者68例,处方剂量为50 Gy分25次.筛选19例患者分别提取其靶区及危及器官有效特征值构成向量,并将每例患者计划的最终优化限制条件保存为模板;其次选取15例（10例模板库中计划和5例模板库外计划）直肠癌患者进行自动优化验证.根据多维向量相似性原理,定义相似性参数 α.设计程序自动从模板库中选择除自身模板外最优计划模板进行自动计划设计.将利用最优模板进行自动计划设计放疗计划（ATP）与临床应用计划（CP）进行剂量学验证,配对样本t检验比较、Pearson相关性分析剂量参数与相似性参数 α 的相关性.对相关剂量参数与 α 进行最小二乘法线性拟合,探索相关参数伴随 α 变化的ATP相对于CP的变化趋势.结果 13例ATP剂量学结果整体略差于CP结果[适形指数（P=0.004）、均匀指数（P=0.015）、小肠V40（P=0.003）、小肠Dmean（P=0.022）].13例患者 α 值分别为2.67、2.60、2.60、2.49、2.67、2.74、2.72、2.48、2.53、2.86、2.68、2.56、2.63;α 与膀胱V40和Dmean具有显著的相关性（r=0.649、0.603,P=0.016、0.029）;仅小肠V40和Dmean伴随 α 增大ATP相对于CP逐渐变差,其余参数均伴随 α 值的增大,使用ATP接近并优于CP.结论 ATP所得结果略差于CP,但能够满足临床要求.需要进一步优化模板库和模板质量以及优化最优模板筛选方法进行探索可能.

Objective To explore the feasibility of the volume modulated arc therapy （ VMAT） auto-planning based on template library （ TL）. Methods VMAT plans of 68 patients diagnosed with postoperative rectal cancer in Eclipse system were retrospectively selected. The prescription dose was 50 Gy/25F. In 19 patients, the feature values of target and organs at risk were extracted as the vectors. The final optimized restricted conditions were saved as the TL. Then, the plans of 15 rectal cancer patients （10 cases from TL and 5 outside TL） were automatically optimized. According to the multi-dimensional vector similarity principle, the similarity parameter αwas defined. The designed program automatically selected the optimal-object template in an in-house software developed with Matlab. The dosimetric parameters of the auto-optimized plans with the optimal-object template （ATP） and the clinical plan （CP） were compared by the paired t-test. The changes in the dosimetric parameters and similarity parameter α were statistically compared by Pearson′s correlation analysis. The linear fitting of the dosimetric parameters with α was used by least squares method to explore the tendency of the ATP dosimetric parameters relative to CP. Results The dosimetric parameters of ATP for 13 cases were slightly worse than those of CP. The conformal index （P=0. 004）, heterogeneous index （P= 0. 015）,V40（P= 0. 003） and mean dose （P= 0. 022） of the intestine significantly differed. The α values of these 13 cases were 2. 67,2. 60,2. 60,2. 49,2. 67,2. 74,2. 72,2. 48, 2. 53,2. 86,2. 68,2. 56 and 2. 63. The α value was significantly correlated with the V40 or mean dose of the bladder （r= 0. 649 and 0. 603,P= 0. 016 and 0. 029）.Along with the increase of α value ,V40 and mean dose of the intestine for ATP were gradually deteriorated than those of CP . The remaining dosimetric para-meters of ATP were close to or superior to those of CP. Conclusions The results of ATP are slightly worse than those of CP, whereas can satisfy the clinical requirements. The TL, the quality of TL and ATP remain to be further optimized.