VMAT下肺等效均匀剂量预测RP价值研究

Clinical value of lung equivalent uniform dose in predicting VMAT-induced radiation pneumonitis

目的 对VMAT下基于肺等效均匀剂量的放射性肺炎预测价值的临床应用效果进行评价及最优化a值的搜寻.方法 选取2015-2016年间接受过VMAT的65例肺癌患者,根据放疗结束后有无RP分成两组,导出DVH等信息,用自编数值分析程序进行数据分析.分别计算a在-50~50区间两组肺等效均匀剂量值变化,找出两组相对肺等效均匀剂量值差距最大的a值.采用成组t检验对发生和未发生放射性肺炎的V5、V20、V30、MLD和肺等效均匀剂量（aoptimal）进行分析;采用Pearson相关分析法分析Vdose和肺等效均匀剂量（aoptimal）与RP之间关系;采用 Logistic回归方法建立疾病预测模型.结果 a=0.3时发生和未发生组肺等效均匀剂量相对差取得最大值（627.94 cGy和510.23 cGy,相对剂量差R=23.07%）.相对差R在-50^-5区间缓慢减少,在-5~0急剧增加且在a=0.3时取得最大值;在a从0.3~4.0区间快速减小后直到研究终点50都趋于缓慢减小趋势.传统物理容积剂量阈值相关性分析也提示肺等效均匀剂量（a=0.3时）和V5、V10、V20、MLD有相关性（r=0.929,P＜0.05）.结论 采用VMAT技术进行胸部肿瘤放疗患者,肺等效均匀剂量（a=0.3时）能较好区分有无肺炎两组,建议肺等效均匀剂量限制在510 cGy内,肺等效均匀剂量和常规物理剂量相结合对非均匀照射条件下RP有一定临床预测价值.

Objective To investigate the clinical effect of lung equivalent uniform dose （LEUD）-based predictive model for radiation pneumonitis （RP） induced by volumetric modulated arc therapy （VMAT） and to determine the optimal a value.Methods A total of 65 patients with primary lung cancer who received VMAT from July 2015 to February 2016 were divided into RP group and non-RP group according to the presence or absence of RP after radiotherapy.Their dose-volume histogram （DVH） data and other data were obtained and analyzed by the self-compiled numerical analysis program.The LEUD values in the two groups were calculated at a=[-50, 50], and then the a value was identified when the relative difference of LEUD between the two groups was maximal.The paired t test was used for analyzing the differences in V5, V20, V30, minimum lethal dose （MLD）, and LEUD （aoptimal） between the two groups.A Pearson correlation analysis was used to determine the correlation of Vdose and LEUD （aoptimal） with RP.The logistic regression method was used to establish the predictive model of RP.Results The maximum relative difference in LEUD between RP group and non-RP group was obtained at a=0.3（627.94 cGy vs.510.23 cGy, relative difference[R]=23.07%）.R decreased slowly at t=[-50,-5], increased sharply at t=[-5, 0], and reached the maximum value at a=0.3.After a rapid decrease at a=[0.3, 4], R decreased slowly at a=[4, 50].The correlation analysis of the traditional physical volume dose threshold also showed that the LEUD （at a=0.3） was correlated with V5, V10, V20, and MLD （r=0.929, P〈0.05）.Conclusions For patients receiving VMAT for thoracic cancer, LEUD （at a=0.3） can distinguish between patients with and without RP.Therefore, LEUD is recommended to be〈510 cGy.A combination of LEUD and conventional physical dose has a good clinical predictive value for RP under non-uniform irradiation.