Multivariate Analysis of Effective Dose and Size-Specific Dose Estimates for Thorax and Abdominal Computed Tomography

The study aimed to compute the effective dose (E) and size-specific dose estimate (SSDE) of routine adult patients undergoing thorax and abdominal computed tomography (CT) imaging and to present their multivariate analysis. All adult thorax and abdominal CT examinations conducted from March 2022 to June 2022 were prospectively included in this study. The Water Equivalent Diameter (D_w) and SSDE of all the examinations were computed from CT dose index volume (CTDI_vol) and Dose length product (DLP) displayed on the dose report in the CT console. The multivariate statistical analysis was performed to investigate the correlation of SSDE and E on CTDI_vol, D_w area of the region of interest (ROI) (Area_ROI), body mass index (BMI), conversion factor (f_size) and hounsfield (HU_mean) number in the ROI at 95% level of significance (P < 0.05). The linear regression analysis was performed to investigate the dependence of SSDE and E on other parameters for both abdominal and thorax patients. A total number of 135 (Abdomen = 61 and Thorax = 74) measurements were performed. The mean value of effective dose for abdomen and thorax patients was found to be 7.17 ± 3.94 and 4.89 ± 2.16 mSv, respectively. The SSDE was observed to be 13.24 ± 3.61 and 13.04 ± 3.61 mGy for thorax and abdomen respectively. The multivariate analysis suggests that SSDE for abdominal CT is found significantly dependent on CTDI_vol, D_w and f_size with P < 0.05 and E is found to be significantly dependent on DLP, Area_ROI, D_w and f_size at 95% level of confidence for abdominal CT imaging. SSDE for thorax CT was found significantly dependent on BMI, CTDI_vol, HU_mean, D_w and f_size at 95% level of confidence. Furthermore, E was observed dependent on DLP at P < 0.05. The linear regression analysis also shows that E is strongly correlated with DLP (r = 1.0) for both thorax and abdominal CT, further the SSDE was observed strongly correlated with CTDI_vol with r = 0.79 and r = 0.86 for abdomen and thorax CT respectively. A strong correlation was observed between BMI and for D_w abdominal CT imaging (r = 0.68). The mean value of SSDE for thorax is slightly greater than abdomen. The average value of effective dose for abdomen and thorax measurements was found to be 7.17 ± 3.94 and 4.89 ± 2.16 mSv and , correspondingly. SSDE for both abdomen and thorax CT is significantly dependent on CTDI_vol, D_w and f_size at 95% level of confidence. The strong correlation was also observed E on DLP and SSDE on CTDI_vol for both Abdomen and Thorax CT. The strong dependence of D_w on BMI (r = 0.68) is due to the excessive fat concentration around the stomach and abdomen.