Renal Stone Patients Overexposed to Radiation?

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Radiation dose found to exceed recommended occupational exposure in 20% of patients.

SHANGHAI, China—Researchers who studied radiation exposure among patients being evaluated for urolithiasis found that about one fifth of them received potentially dangerous radiation doses.

Investigators at Duke University Medical Center in Durham, N.C., and the University of Texas Southwestern Medical Center in Dallas identified 108 patients who underwent radiologic imaging for renal stones. The patients had an average of four radiographic exams over one year of follow-up, including an average of 1.2 KUBs, 1.7 abdomino-pelvic CTs, and one IV urogram.

The median effective radiation dose per patient was 29.7 mSV. Twenty-two patients (20%) received more than 50 mSv, which according to the International Commission on Radiological Protection is the recommended yearly maximum occupational radiation exposure. CT was associated with the greatest radiation exposure. The investigators believe the highest exposures were among individuals who were recurrent stone formers.

Lead investigator Michael Ferrandino, MD, who presented results here at the 2008 World Congress of Endourology, said he and his co-investigators were not surprised by the findings.

“We figured it was going to be a good percentage of patients, based on how commonly CT is used for renal colic and stones,” said Dr. Ferrandino, a clinical associate in laparoscopy and endourology at Duke. “Don't forget, though, that ‘maximum radiation exposure' is an occupational guideline and not a clinical/diagnostic one. These patients had good reasons to undergo their studies.”

Raymond Leveille, MD, professor of clinical urology and chief of the Division of Endourology and Laparoscopy at the University of Miami, said the findings by Dr. Ferrandino's team may have important clinical implications. “Since seeing this poster, I have started thinking about the radiation dosage a lot more,” Dr. Leveille said.

“I've already spoken to our radiology department to see if we can use a lower dose of radiation for kidney-stone patients, and we're going to come up with a protocol here at the University of Miami to implement that includes alternatives [to CT scans] wherever possible.” He said he plans to use combinations of plain radiographs and ultrasonography.

In a recently published study in the Journal of Endourology (2008;22:419-422), Babbin John, MRCS, specialty trainee in urology at Kent and Canterbury Hospital, Canterbury, U.K., and two other researchers from St. George's Hospital, London, reported that the average radiation exposure associated with a single stone episode is 5.3 mSv.

In an interview with Renal & Urology News, Dr. John suggested that the new findings be interpreted with caution. “We must also not lose sight of the fact that the study results are from two major stone-treatment centers in the United States that almost certainly will be dealing with tertiary referrals and complex stone disease,” Dr. John said.

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