Unenhanced CT as the sole initial diagnostic investigation for acute renal colic patients: ureteric stone size and radiation risks consideration

Abstract

Objective: To compare the detectabilities of ureteric stones in non-contrast computed tomography (NCCT) and planar radiography of kidney, ureters and bladder (KUB), and to evaluate its associated radiation risks.

Patients & Methods: A total of 106 patients who underwent NCCT and KUB for acute renal colic from Jan 2011 to Feb 2012 were reviewed and analyzed with paired t-test. Patient organ radiation absorbed doses were measured with the use of 35 lithium fluoride thermoluminescent dosimeters (TLD) chips inside an Alderson-Rando standard adult phantom. The patient effective dose was calculated according to the ICRP-103 approach.

Results: Overall ureteric stone detection rate in KUB was 43% of NCCT. NCCT significantly detected smaller (<=5 mm) ureteric stones when compared to KUB (p < 0.05). Patient effective doses in NCCT were calculated as 10.1 mSv for male and 12.2 mSv for female. The calculated cancer induction risk would not be more than 0.8 cases in 1000 patients for each NCCT in renal colic. The calculated hereditary effect would not be more than 0.028 cases in 1000 patients.

Conclusion: Our unenhanced CT protocol is safe and superior to KUB in diagnosing ureteric stones. We recommend unenhanced CT as the first line imaging investigation for acute renal colic patients.