有无均整器模式下海马保护全脑放疗剂量学比较

Dosimetric comparison of hippocampal avoidance wholebrain radiotherapy with flattening filter and flattening filter-free modes

目的探讨采用有均整器(FF)和无均整器(FFF)模式下容积旋转调强在海马保护性全脑放疗中的剂量学差异。方法选取15例海马保护全脑放疗患者,对每例患者设计FF-VAMT和FFF-VMAT 2种放疗计划,达到临床剂量要求前提下,进行剂量学、机器总跳数、出束总时间比较。结果2种计划相比,在靶区覆盖率、适形度和剂量梯度上的差异无统计学意义(P>0.05)。在海马体组织D_(max)、D_(100%)、D_(mean)3项剂量参数上,FFF-VAMT计划可分别控制在(15.13±0.38)Gy、(7.12±0.34)Gy和(9.76±0.43)Gy,明显小于FF-VAMT计划的(16.46±0.56)Gy、(7.72±0.28)Gy、(10.54±0.48)Gy,差异均有统计学意义(P<0.05);左右晶体的D_(max)与眼球D_(mean)分别为(7.26±0.43)Gy、(6.29±1.13)Gy、(11.01±0.94)Gy、(9.78±1.13)Gy明显小于FF-VAMT计划(8.09±0.66)Gy、(7.80±0.74)Gy、(11.38±1.09)Gy、(11.05±0.90)Gy(P<0.05)。其它危及器官如视神经视交叉等剂量均控制在临床安全剂量范围内,且两计划之间差异无统计学意义(P>0.05);FFF-VAMT计划MU值大于FF-VMAT计划,出束时间小于FF-VMAT计划,差异有统计学意义(P<0.05)。结论FF-VAMT和FFF-VAMT 2种放疗方式均能满足临床需求,FFF-VAMT放疗方式对海马体和晶体的保护上更具优势,且FFF模式出束时间短,治疗效率高。

Objective To compare the dosimetric differences of volumetric modulated arc therapy(VMAT)with flattening filter(FF)and flattening filter-free(FFF)modes in hippocampal avoidance whole brain radiotherapy.Methods We included 15 patients with hippocampal-sparing whole brain radiotherapy,and designed two radiotherapy plans of FF-VMAT and FFF-VMAT for each patient.On the premise of meeting clinical dose requirements,the two plans’dosimetry,total number of monitor units,and beam-on time were compared.Results There were no significant differences in the target coverage,conformity index,and dose gradient of the FF-VMAT and FFF-VMAT plans(P>0.05).The D_(max),D_(100%),and D_(mean)to the hippocampal tissue were significantly lower with FFF-VMAT[(15.13±0.38)Gy,(7.12±0.34)Gy,and(9.76±0.43)Gy,respectively than with FF-VMAT(16.46±0.56)Gy,(7.72±0.28)Gy,and(10.54±0.48)Gy,respectively](P<0.05).The D_(max)to the left and right lenses and the D_(mean)to the left and right eyeballs with FFF-VMAT were(7.26±0.43)Gy,(6.29±1.13)Gy,(11.01±0.94)Gy,and(9.78±1.13)Gy,respectively,which were significantly lower than FFVMAT’s corresponding doses of(8.09±0.66)Gy,(7.80±0.74)Gy,(11.38±1.09)Gy,and(11.05±0.90)Gy,respectively(P<0.05).The doses to other organs at risk including the optic nerve and optic chiasm were all controlled within the safe dosage ranges,with no significant differences between the two plans(P>0.05).The FFF-VMAT plan had a significantly greater number of monitor units and a significantly shorter beam-on time than the FF-VMAT plan(P<0.05).Conclusion Both FF-VMAT and FFF-VMAT can meet the clinical requirements,with FFF-VMAT having better hippocampus and lens protection,shorter beam-on time,and higher treatment efficiency.