Low-dose unenhanced CT protocols according to individual body size for evaluating suspected renal colic: cumulative radiation exposures

Abstract

Purpose: The aim of this study was to assess the radiation dose of dose-reduced unenhanced abdominal multidetector computed tomography (MDCT) scan protocols for suspected renal colic in patients within normal weight range and overweight-obese patients and to record the cumulative dose of repeated examinations.

Materials and methods: Over a 2-year period, we performed 1,026 unenhanced CT examinations for urolithiasis; among these, 675 were performed on 636 patients referred from the emergency department. Patients were divided into two groups on the basis of body mass index (BMI): normal weight (BMI <25 kg/m(2) group 1); overweight and obese (BMI >25 kg/m(2) group 2). For patients in group 1 and group 2, the protocols of our 64-row scanner prescribe tube current settings at 70 mAs and 150 mAs, respectively. The dose-length product (DLP) estimated by using the manufacturer's software was converted into effective dose (ED).

Results: Mean DLP and ED were 177 and 345 mGy/cm and 2.4 and 4.8 mSv for group 1 and group 2, respectively. A subset of 25 patients (3.7%) underwent two or more examinations, with estimated ED ranging from 4.8 to 19.2 mSv.

Conclusions: Although radiation dose is nearly double in overweight-obese patients undergoing MDCT, it remains lower than that delivered by a standard-dose protocol. Patients with flank pain, who are often young, are at increased risk for serial CT examinations. Use of a low-dose protocol is mandatory in both normal-weight and obese patients to minimise radiation exposure.