摘要目的 比较加速器6MVX射线非均整模式(FFF)和均整模式(FF)下局部进展期鼻咽癌容积调强(VMAT)计划的剂量学差异.方法 选取10例已行放疗的局部进展期鼻咽癌患者,分别设计FFF和FF VMAT计划,在满足临床要求的情况下,比较两种计划的剂量体积直方图(DVH)、靶区剂量分布、危及器官受量、靶区适形度、总机器跳数和治疗时间.结果 两者均能满足临床治疗需求,FFF VMAT计划靶区最大剂量和平均剂量大于FF VMAT计划(t=-0.31、-0.35,P ＜0.05),而计划靶区适形度略低(t=5.42,P＜0.05),左右晶状体的最大剂量低于FF VMAT计划(t=25.87、17.45,P＜0.05),其他危及器官剂量无明显差异.机器总跳数FFF VMAT为(699±16) MU,FFVMAT为(628±12)MU.平均单次治疗时间均约2 min,两者无明显差别.结论 两种计划均能满足临床治疗需求,FFF VMAT计划更利于保护照射野边缘危及器官,如晶状体.机器总跳数FFFVMAT计划高于FF VMAT计划但两者平均单次治疗时间无明显差别.

abstractsObjective To compare the dosimetric difference of volumetric modulated arc therapy (VMAT) plans for the loco-regionally advanced nasopharyngeal carcinoma (NPC) patients using 6 MV X-ray flattening filter-free (FFF) and flattening filter (FF) modes.Methods Ten previously treated patients with loco-regionally advanced nasopharyngeal carcinoma were retrospectively included and replanned using FFF and FF VMAT,respectively.Meeting all clinical criteria,the dose-volume histograms (DVH),dose distribution of target volume and organs at risk (OARs),target conformity index (CI),total monitor unites (MUs) and treatment time were compared across the plans.Results VMAT plans suing either FFF and FF modes can meet the clinical objectives.The maximum and mean target dose of FFF VMAT plans were significantly higher than that of FF VMAT plans (t =-0.31,-O.35,P ＜ O.05).Yet the planning target volume (PTV) CI of FF mode was slightly better than of FFF mode (t =5.42,P ＜0.05).The maximum doses of lenses in FFF VMAT plans were lower than that of FF VMAT plans (t =25.87,17.45,P ＜ 0.05),and other OARs displayed no significant difference.The mean total MUs of FFF and FF VMAT plans were (699 ± 16) and (628 ± 12) MUs respectively.The mean treatment time of two modes were consistent (about 2 min).Conclusions The plan qualities of FFF and FF VMAT plans were comparable and both clinically acceptable.The OARs at the edge of radiation field,such as lens,could be spared better using FFF VMAT mode.The total MUs of FFF VMAT plans were higher than FF VMAT plans,yet were delivered within the same time.