AUA 2019: Radiation Dose Reduction of Unenhanced CT Scan Limited to the Kidneys for Follow-up of Asymptomatic Patients with Known Nephrolithiasis

Chicago, IL ( Radiation exposure is a rising concern as the utilization of medical imaging has skyrocketed with advents in imaging technology. It is estimated that nearly 1-2% of all cancers are due to iatrogenic exposure. It is imperative that healthcare providers be advocates of the ALARA (As Low As Reasonably Achievable) principle.

Non-contrast computed tomography (NCCT) is the imaging modality of choice for evaluating nephrolithiasis. Patients with recurrent nephrolithiasis may potentially undergo multiple NCCT during their lifetime. Standard NCCT for stone evaluation involves imaging of the entire abdomen and pelvis.

Canvasser and colleagues sought out to identify specific bony landmarks (and associated radiation dose reduction) to potentially limit CT scanning to only the kidneys. They conducted a retrospective study of 299 patients who underwent the standard non-enhanced CT abdomen and pelvis. They recorded total z-axis lengths and also radiation doses for the standard scan. They also recorded new z-axis lengths by recording only the upper and lower limits of the kidneys on each scan. Utilizing computer software they were able to provide organ equivalent radiation doses for both the standard CT and their new limited CT.

For standard CT, the average z-axis length was 47 cm. The average z-axis length of the new limited CT was reduced by about 50%. When using the superior endplate of T10 as the upper limit of the scan and using the inferior endplate of L5 as the lower limit, they were able to include all 299 patients’ kidneys. The whole body radiation dose exposure was reduced by 41% and organ specific doses for breast (72%), gonadal (74%), and bladder (82%) were all reduced significantly.


Canvasser and colleagues undertook a very important study that showed up to 41% reduction of whole body radiation dose exposure for patients getting CT scans. Although standard CT scans may reveal incidental findings, this sizable reduction may be applicable to recurrent stone formers who may not necessarily need a more broad-encompassing scan.

Presented by: Noah Canvasser, MD, Assistant Professor, Department of Urology, UC Davis Health, Sacramento, California, United States

Written by: John Sung (@JohnM_Sung), Medical Student Texas A&M University, College of Medicine, Dallas, Texas, Research Fellow, University of California, Irvine Department of Urology at the American Urological Association's 2019 Annual Meeting (AUA 2019), May 3 – 6, 2019 in Chicago, Illinois