Abstract
Purpose:To determine the quantitative effect of adipose tissue shielding on organ dose measurements in computed tomography (CT) and model the effects with organ dose equations.Methods:The post‐mortem dose measurement methodology established in house was utilized to perform organ dose measurements on subjects of varying body habitus for a clinically standardized chest/abdomen/pelvis (CAP) protocol and chest protocol on a 320‐slice CT scanner. The outer effective diameter was calculated obtaining the anterior/posterior and lateral dimensions of the entire anatomy imaged at the middle of the scan range, while the inner effective diameter used the AP and Lat dimensions of the anatomy excluding adipose tissue. These parameters determined effective diameter using Effective Diameter= SQRT(AP *Lat). The subjects were matched by their inner effective diameter and the effective shielding radius was calculated by subtracting the inner effective diameter from the outer effective diameter and dividing by two. The relationship to organ specific CTDI‐to‐organ dose conversion factors was analyzed using linear regression analysis.Results:Of 7 subjects scanned with both the CAP and chest protocols, three were found to have the same inner effective diameters. The calculated CTDI‐to‐organ‐dose conversion factors relationship with the effective internal shielding radius was analyzed using a linear regression analysis. The R2 value for organs within the inner effective diameter space to include lungs, liver, stomach, small intestine, colon, uterus, and ovary ranged from 0.74 to 0.99, with an average of 0.91 for the CAP equations. While the R2 values for the chest scans for lungs, liver, and stomach ranged from 0.98 to 0.9991 with an average of 0.99, showing a good linear fit.Conclusion:The effective internal shielding radius shows a strong correlation when matching similar inner effective diameters to the CTDI‐to‐organ‐dose conversion factors.
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