Size-Specific Dose Estimates of Radiation Based on Body Weight and Body Mass Index for Chest and Abdomen-Pelvic CTs.

Background. To correlate body weight, body mass index (BMI), and water-equivalent diameter (dw) and to assess size-specific dose estimates (SSDEs) based on body weight and BMI for chest and abdomen-pelvic CT examinations. Methods. An in-house program was used to calculatedw, size-dependent conversion factor (f), and SSDE for 1178 consecutive patients undergoing chest and abdomen-pelvic CT examinations. Associations among body weight, BMI, anddwwere determined, and linear equations were generated using linear regression analysis of the first 50% of the patient population. SSDEs (SSDEweight and SSDEBMI) were calculated based on body weight and BMI asdwsurrogates on the second 50% of the patient population. Mean root-mean-square errors of SSDE(weight)and SSDE(BMI)were computed with SSDE from the axial images as reference values. Results. Both body weight and BMI correlated strongly withdwfor the chest (r=0.85, 0.87, all p<0.001) and abdomen-pelvis (r=0.85, 0.86, all p<0.001). Mean values of SSDEweight and SSDEBMI based on the linear equations for body weight, BMI, and d(w) were in close agreement with SSDE from the axial images, with overall mean root-mean-square errors of 0.62 mGy (6.10%) and 0.57 mGy (5.65%), for chest, and 0.76 mGy (5.61%) and 0.71 mGy (5.22%), for abdomen-pelvis, respectively. Conclusions. Both body weight and BMI, serving asdwsurrogates, can be used to calculate SSDEs in the chest and abdomen-pelvis CT examinations, providing values comparable to SSDEs from the axial images, with an overall mean root-mean-square error of less than 0.76 mGy or 6.10%.