CT辐射剂量指数的修正和快速转换因子的探讨

Correction of CT radiation dose index and study on fast conversion factor

目的探讨临床常见CT扫描部位中不同尺寸参量对体型特异性剂量估算(SSDE)的影响,以建立SSDE的快速转换因子。方法于2021年3月8日至5月10日在首都医科大学附属北京同仁医院收集颅脑、鼻骨、鼻窦、颈部、胸和腹盆6个临床常见扫描部位共189个临床病例。利用Matlab自编程序进行批量图像处理,计算横断面图像的面积、前后径、左右径以及平均CT值信息,由病例的真实有效直径和水当量直径得到估算体型特异性剂量值的转换因子,并比较两种特异性剂量估计SSD_(EED)和SSDE_(WED)值的差异。根据临床实践中便于得到的前后径、左右径、前后径+左右径、估算有效直径,以及程序所得真实有效直径和水等效直径,建立便于应用的成年人各部位SSDE快速修正因子。得出水当量直径和有效直径的便捷转换关系。以水当量直径对应的修正因子为基准,比较各种尺寸参量对应的修正因子之间的相对误差。结果颅脑、鼻骨、鼻窦、颈部、胸部和腹盆6个CT检查部位的真实有效直径对应的SSDE快速转换因子分别为1.01、1.01、1.01、0.97、1.28、1.32,水当量直径对应的SSDE快速转换因子分别为0.87、0.97、0.98、0.99、1.42、1.36。不同类型转换因子之间相对误差变化范围为0.68%~18.05%。腹盆部的各种尺寸参量的转换系数相差最小,胸部的前后径和左右径对应的转换系数误差最小。颅脑使用左右径对应的转换系数误差最小。鼻窦、胸部和腹盆的CTDI_(vol)与SSD_(EED)和SSDE_(WED)比较,差异均有统计学意义(t_(鼻窦)=2.44、4.23,t_(胸部)=17.67、17.00,t_(腹盆)=17.93、18.75,P<0.05);颅脑和鼻骨的CTD_(Ivol)与和SSDE_(WED)比较差异有统计学意义(t=-22.27、2.80,P<0.05),与SSD_(EED)比较差异无统计意义(P>0.05);而颈部CTDI_(vol)与SSD_(EED)比较差异有统计学意义(t=-3.06、P<0.05),与SSDE_(WED)比较差异无统计意义(P>0.05)。结论SSDE_(WED)可以更加精准的评估受检者的体型特异性剂量,不同扫描部位可选择不同的尺寸参数进行修正。快速转换因子可便捷用于临床操作,提高受检者辐射剂量估计的准确性。

Objective To explore the influence of different size related parameters of common CT scanned body parts on body-specific dose estimate(SSDE),in order to establish rapid conversion factors for SSDE.Methods A total of 189 clinical cases were collected from 6 common CT scanned body parts,including head,nasal bone,sinus,neck,chest,abdomen and pelvis,at Beijing Tongren Hospital,Capital Medical University from March 8 to May 10,2021.Batch-processing of image was carried out by using Matlabcode.The axial images′area,anteroposterior(AP)dimension,lateral(LAT)dimension and average CT values were calculated.The conversion factors for estimating body-specific dose values were obtained from the real effective diameter(De)and water equivalent diameter(Dw)of the clinical cases,and the differences in values were compared between SSD_(EED) and SSDE_(WED).Based on the information on AP,LAT,AP+LAT,estimated De,the real De and Dw obtained in clinical practices,the SSDE rapid correction factors for adult body parts were established.The convenient conversion relation between Dw and De was obtained.Based on the correction factors for Dw,the relative errors of the correction factors for various sizes related parameters were compared.Results The SSDE fast conversion factors for the real De of the 6 body parts were 1.01,1.01,1.01,0.97,1.28,1.32,and those for Dw were 0.87,0.97,0.98,0.99,1.42,1.36,respectively.The relative errors of different conversion factors ranged from 0.68%to 18.05%.The conversion factors for abdomen and pelvis had the smallest difference,and those for AP and LAT of the chest had the smallest error.The differences between CTDIvol,SSD_(EED) and SSDE_(WED) in sinus,chest and abdomen were statistically significant(t sinus=2.44,4.23,t chest=17.67,17.00,t abdomen and pelvis=17.93,18.75,P<0.05).The differences between CTDIvol and SSDE_(WED) in head,nasal bone,were statistically significant(t=-22.27,2.80,P<0.05),but not with SSD_(EED)(P>0.05).The difference between CTDIvol and SSD_(EED) in neck was statistically significant(t=-3.06,P<0.05)but without statistical insignificance in camparison with SSDE_(WED)(P>0.05).Conclusions SSDE_(WED) can be used to accurately evaluate the body-specific dose estimatates,and different size related parameters can be selected for correction in different scanned body parts.The rapid conversion factor can be easily used in clinical practice to improve the accuracy of estimated radiation dose.