中心层左右径在儿童胸部CT体型特异性剂量测量中的应用

Application of the size-specific dose estimate based on the left-right diameter of central plane of chest CT in children

目的:比较容积CT剂量指数(CTDIvol)与体型特异性剂量估算(SSDE)两种测量方法测得的辐射剂量在儿童胸部CT检查中的差异。方法:回顾性分析2020年1月至2021年8月行胸部CT检查的131例儿童的病例资料,所有患儿图像均能满足诊断要求。根据患儿图像中心层面的左右径(LAT)进行分组:A组LAT<20 cm, 22例;B组20≤LAT<23 cm, 20例;C组23≤LAT<26 cm, 21例;D组26≤LAT<29 cm, 25例;E组29≤LAT<32 cm, 23例;F组LAT≥32 cm, 20例。测量患儿胸部中心层CT图像的最大左右径,手动勾画体表最小的范围,不包括检查床床板,测量平均CT值、面积,记录患儿的CTDIvol,并计算转换因子fWED和SSDE,比较CTDIvol与SSDE的差异。结果:各组的左右径(LAT)、转换因子(fWED)、水当量直径(WED)差异均有统计学意义(P值均<0.05)。6组CTDIvol与SSDE差异度依次为223.06%、213.01%、203.44%、181.58%、173.58%、157.87%。各组CTDIvol与SSDE均呈正相关。结论:儿童胸部CT检查中,CTDIvol较SSDE低估了患儿的辐射剂量,且患儿中心层面左右径越小,被低估的辐射剂量越大。

Objective:The pupose of this study was to compare the difference of radiation dose measured by volume CT dose index(CTDIvol) and size-specific dose estimate(SSDE) in children’s chest CT.Methods:A retrospective analysis was conducted on the data of 131 children who underwent chest CT scan from January 2020 to August 2021,and all images could meet the diagnostic requirements.All subjects were divided into diffrent groups according to the left-right(LAT) sizes at the central plane: group A,22 cases with LAT<20cm, group B,20 cases with 20≤LAT<23cm, group C,21 cases with 23≤LAT<26cm, group D,25 cases with 26≤LAT<29cm, group E,23 cases with 29≤LAT<32cm, group F,20 cases with LAT≥32cm.The maximum diameter of LAT of each patient was measured on the central CT plane, and the minimum range of body surface was delineated manually, excluding the bed board.The average CT value and area were measured, and CTDIvol, fWEDand SSDE of each patient were recorded and calculated.The differences between CTDIvol and SSDE were compared.Results:There were significant differences in the LAT,fWEDand water equivalent diameter(WED) among all groups(P<0.05).The variability between CTDIvol and SSDE of 6 groups were 223.06%,213.01%,203.44%,181.58%,173.58% and 157.87%,respectively.CTDIvol was positively correlated with SSDE in each group.Conclusions:In chest CT scan of children, CTDIvol underestimate the radiation dose compared with SSDE,and the smaller LAT diameters of the central plane, the greater the underestimated radiation dose.