摘要目的 比较鼻咽癌非均整(FFF)与均整(FF)模式下VMAT计划剂量学特性,分析FFF模式下VMAT计划临床可行性.方法 选取2016-2017年间Ⅱ期鼻咽癌患者10例,分别对同一患者CT图像及CTV用相同处方剂量6 975 cGy和相同优化参数在RayStation计划系统平台设计6 MVX射线FFF和FF的VMAT计划,比较两种计划剂量学特性、机器跳数和出束时间.配对￡检验差异.结果 FF计划与FFF计划的靶区D98％、靶区覆盖率、CI均相近(P=0.262～0.975),FF计划在靶区D2％、Dmean、HI略有优势(P=0.004～0.038);FFF计划较FF计划在左、右眼晶体受量、左腮腺受量＞30 Gy体积、左颞叶Dmean有一定降低(P=0.002～0.025);正常组织(Body)在2～ 30 Gy内FFF计划受照体积均＜FF计划(P=0.000～0.003);FFF计划平均机器跳数增至FF计划的1.188倍(P=0.000),平均出束时间减少为FF计划的91.2％(P=0.024).结论 FF计划和FFF计划均能满足临床剂量学要求.在靶区剂量分布上FF计划略有优势,在OAR保护和低剂量照射上FFF计划更具优势,虽然FFF计划机器跳数增加,但出束时间反而下降,因此FFF模式可能有利于提高治疗效率.

abstractsObjective To compare the dosimetric characteristics of the VMAT plans between the flattening-filter-free (FFF) and flattening filter (FF) modes for nasopharyngeal carcinoma and analyze the feasibility of VMAT plans in the FFF model applied in clinical practice.Methods Ten patients diagnosed with stage Ⅱ nasopharyngeal carcinoma between 2016 and 2017 were recruited in this investigation.For the CT image and clinical target volume (CTV) of the identical patient,FFF-and FF-mode VMAT plans were established with the identical prescription dose of 6 975 cGy and the identical modified parameters on the RayStation platform (6 MV X-ray).The dosimetric characteristics,the number of machine hops and the time of beam were recorded and statistically compared between the FFF and FF modes.Results The minimum dose D98％ target,target coverage,conformal index (CI) did not significantly differ between the FF and FFF plans (P=0.262-0.975),whereas the maximum dose of D2％,the average dose of D and target homogeneity index (HI) of the FF plans were slightly advantageous to those of the FFF plan (P=0.004-0.038).The acceptable dose of bilateral lenses,the volume of the left parotid gland with an acceptable dose of＞ 30 Gy and the average dose of the left temporal lobe in the FFF mode were declined compared with those in the FF mode (P=0.002-0.025).The volume of normal tissues (Body) within the dose range of 2-30 Gy in the FFF mode was less than that in the FF mode (P=0.000-0.003).In the FFF mode,the mean number of machine hops was 1.188 times (P=0.000) and the average time of beam was 91.2％ of the FF plan (P=0.024).Conclusions Both the FF and FFF plans qualify the dosimetric requirements in clinical settings.FF plan is advantageous in terms of the dose distribution in the target area,whereas FFF plan yields better OAR protection and low-dose irradiation.In spite of the increasing quantity of machine hops,the time of beam is declined in the FFF plan.Consequently,FFF mode probably contributes to enhance the clinical efficacy.