The Evaluation of the Effective Diameter (Deff) Calculation and its Impact on the Size-Specific Dose Estimate (SSDE)

Abstract

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 compared 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