The Evaluation of the Effective Diameter (<em>D_eff</em>) Calculation and its Impact on the Size-Specific Dose Estimate (<em>SSDE</em>)

Information on the effective diameter ( D eff ) is essential for estimating the dose for patients undergoing CT examinations. The purpose of this study was to calculate the effective diameter using the maximum values of lateral (LAT) and anterior-posterior (AP) diameters ( D eff,m ) and using LAT and AP diameters taken from the center of the image ( D eff,c ), and compare d both estimates to the effective diameter calculated directly from the cross-sectional area of the patient ( D eff,A ). We evaluated 164 patients who underwent the four most frequent CT examinations, namely pelvic, abdominal, thoracic, and head examinations, using a multi-detector CT (MDCT), the Toshiba Aquilion 128. We calculated the percentage differences between D eff,c and D eff,m from D eff,A . We also used the Wilcoxon-Mann-Witney U test to statistically determine whether differences were significant. While D eff,m is statistically no different ( p > 0.05) from D eff,A , D eff,c is statistically different ( p ˂ 0.05) from D eff,A except for head examinations. Received:  31 May 2016 ; Revised:  14 December 2016 ; Accepted:  20 January 2017