Comparison of effective radiation doses in patients undergoing unenhanced MDCT and excretory urography for acute flank pain.

ABSTRACT

OBJECTIVE: The purpose of this study was to measure and compare the effective radiation dose in patients undergoing unenhanced MDCT and excretory urography for acute flank pain, and to explore technical and practical factors affecting the effective dose. SUBJECTS AND METHODS: One hundred nineteen patients with acute flank pain were included. All patients were examined using both MDCT and excretory urography. CT involved one acquisition from the upper kidney margin to the symphysis pubis. The only protocol variation was in the tube current (mAs), which was made according to patient body mass. The excretory urography protocol consisted of three images, with more when supplementary images were needed. Effective radiation doses were computer-simulated using dosimetry programs for CT and conventional radiography, based on Norwegian Radiological Protection Board dose data sets. Mean and SDs of measured patient doses were calculated and compared. Further analyses of dose variations in body mass categories (body mass index) were conducted, as were analyses concerning the number of images taken. RESULTS: The mean effective doses were 7.7 mSv with MDCT and 3.63 mSv with excretory urography. The effective dose varied both in and between techniques but could be predicted. Radiation risk decreased significantly with increased patient weight. CONCLUSION: The average effective dose with MDCT was more than double that with excretory urography. However, the appropriate dose could be strongly predicted by the patient's body mass index and by procedure. An optimum low-dose protocol should be considered before initiating unenhanced MDCT for ureteral colic in order to minimize the radiation-induced cancer risk and to secure adequate image quality.