The concept of low-dose radiation exposure for CT imaging is important, but no quantitative definition exists. There is variability over time with hardware and software changes, geographical variability based on different regulatory bodies and patient body habitus, and conceptual imprecision. Furthermore, the AUA definition of low-dose CT scan is 4 mSv, while the American College of Radiology (ACR) definition is 3 mSV.
According to Dr. Remer, there are several ways to reduce radiation exposure:
- Reduce coverage – only image the top of the kidneys to the bladder base
- Increase slice thickness from 1-3 mm to 5 mm and add coronal reformatted imaging (reduces dose 30-50%)
- Decrease tube current (mAs) – use automated modulation, particularly in obese patients. Small retrospectives studies have shown no significant differences with 50% or 75% mAs reduction for detection of >3mm stones.
- Lower tube voltage (kVp) – dose reduction of 35-75%, although with increased degradation (“noise”)
Dr. Remer concluded with several goals moving forward for renal colic imaging: (i) minimizing unnecessary imaging, (ii) shared-decision making, and (iii) facilitate prompt evaluation. Continued refinement of algorithms for acute colic/known stone formers is necessary and important.
Speaker(s): Erick Remer, Cleveland Clinic Foundation, Cleveland, OH, USA
Written by: Zachary Klaassen, MD, Urologic Oncology Fellow, University of Toronto, Princess Margaret Cancer Centre, Twitter: @zklaassen_md, at the AUA Quality Improvement Summit - October 21, 2017- Linthicum, Maryland
1. Moore CL, et al. Derivation and validation of a clinical prediction rule for uncomplicated ureteral stone – the STONE score: retrospective and prospective observational cohort studies. BMJ 2014;348:g2191.`