ＣＴ 辐射剂量指数的修正和快速转换因子的探讨

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 (D_e) and water equivalent diameter (D_w ) of the clinical cases, and the differences in values were compared between SSDE_ED and SSDE_WED. Based on the information on AP, LAT, AP + LAT, estimated D_e, the real D_e and D_w obtained in clinical practices, the SSDE rapid correction factors for adult body parts were established. The convenient conversion relation between D_w and D_e was obtained. Based on the correction factors for D_w, the relative errors of the correction factors for various sizes related parameters were compared. Results The SSDE fast conversion factors for the real D_e of the 6 body parts were 1.01, 1.01, 1.01, 0.97, 1.28, 1.32, and those for D_w 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 CTDI_vol, SSDE_ED and SSDE_WED in sinus, chest and abdomen were statistically significant (t_smus = 2. 44, 4.23, t _chest = 17.67, 17.00, t abdomen and pelvis = 17.93, 18.75, P<0. 05). The differences between CTDI_vol and SSDE, in head, nasal bone, were statistically significant (t = -22. 27, 2. 80, P<0. 05), but not with SSDE_ED (P>0. 05). The difference between CTDI_vol and SSDE_ED 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.