Doses metrics and patient age in CT

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 (d_w) 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 calculate d_w, size-dependent conversion factor (f), and SSDE for 1178 consecutive patients undergoing chest and abdomen-pelvic CT examinations. Associations among body weight, BMI, and d_w were determined, and linear equations were generated using linear regression analysis of the first 50% of the patient population. SSDEs (SSDE_weight and SSDE_BMI) were calculated based on body weight and BMI as d_w surrogates 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 with d_w for 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 SSDE_weight and SSDE_BMI 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 as d_w surrogates, 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%.