Consider Radiation-Sparing Stone Follow-Up

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Kidney stone disease represents a substantial portion of the urologist's surgical practice.

High recurrence rates, intermittent compliance with stone prevention regimes, and young age at presentation lead to repeated diagnostic imaging with a substantial risk of cumulative radiation exposure for a disease that is inherently benign and rarely life threatening.

During acute episodes of renal colic, the patient invariably presents to the urologist after a non-contrast CT scan of the abdomen and pelvis has accurately determined the number, location, and size of the stone(s).

If ureteroscopy and laser lithotripsy follow, no further preoperative imaging is required, with substantial variability among practitioners in the patient's exposure to intra-operative fluoroscopy.

Alternatively, shock wave lithotripsy (SWL) patients will likely receive an additional preliminary KUB x-ray and/or repeat CT (if the KUB does not demonstrate the stone and a time lag exists between SWL and the previous CT) as well as intra-operative fluoroscopy during SWL targeting.

In either case, after successful treatment of the offending stone(s), repeat imaging to ensure clearance of fragments and the absence of hydronephrosis follows. As the gold standard for the diagnosis of renal and ureteral calculi in the setting of renal colic, CT has now become common for long-term follow-up. CT protocols vary significantly across institutions with the ideal low-dose “CT-KUB” not necessarily used at all imaging centers.

Both compliant patients in structured follow-up programs and non-compliant or marginalized patients accessing the health care system via the emergency department are at risk. The concerned radiologist who tallies the number of studies in a short period of time is increasingly the patient safety advocate.

A recently published study1 from two large U.S. referral kidney stone centers highlights the potential risks to stone patients. In this study, 20% of patients had radiation exposures exceeding the recommended limit of 50 mSv set by the International Commission on Radiological Protection.2

A call to return to KUB x-ray and renal ultrasound radiological follow-up is a logical response, but in this era of burgeoning obesity and increased risk of uric acid stones, low-dose CT will remain central to the long-term follow-up of a substantial portion of stone patients. This study reinforced  previous changes in my practice pattern in which I make a conscious effort to “think before writing.” I take into account the limitations of non-CT imaging (i.e., ultrasound) in each stone patient. I try to lengthen the interval between imaging studies, using estimates of patients' stone recurrence risk as a guide.

I estimate this risk using a combination of prior stone history, metabolic evaluation results, and response to medical intervention. In addition, and equally important, I have regular consultations with my radiology colleagues to keep abreast of current imaging protocols and changes in technology to ensure the best low-dose imaging with the lowest potential risk for my patients.

Take this opportunity to reflect on your pattern of practice for following kidney stone patients and consider adding a trip to the radiology department at your center this week.

Dr. Paterson is assistant professor of urology at the University of British Columbia in Vancouver and a member of the Renal & Urology News editorial board.

References

  1. Ferrandino M, Bagrodia A, Pierre SA, et al. Radiation exposure in the acute and short-term management of urolithiasis at 2 academic centers. J. Urol. 2009;181:668-671.
  2. ICRP Publication 60: 1990 Recommendations of the International Commission on Radiological Protection, 60. Annals of the ICRP vol 21/1-3. Oxford, 1991.
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