ED physicians urged to consider imaging history when ordering CT

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Emergency department (ED) physicians should review a patient's CT imaging history and cumulative radiation dose when considering whether to perform another CT exam, according to a study in the April issue of the American Journal of Roentgenology.

The study included 130 patients who had at least three ED visits within one year in which they had a CT scan of the neck, chest, abdomen or pelvis.

"We gathered the recent CT exam histories for each of these patients and found that half had undergone ten or more CT scans in the previous eight years, up to a maximum of 70 CT scans," said Aaron Sodickson, MD, PhD from the department of radiology at Brigham and Women's Hospital in Boston. "Using typical dose values and standard risk estimation methods, we calculated that half of our group had accrued additional radiation-induced cancer risks above baseline greater than one in 110, up to a maximum of one in 17."

Over the 7.7-year period, the median, mean and maximum values for the study count were 10, 13, and 70 with cumulative CT doses of 91,122, and 579 mSv and lifetime attributable risk of one in 110, one in 82, and one in 17, respectively, according to the researchers. ED studies comprised 55 percent of those captured. Repeat imaging of the same study type represented at least half of the imaging for 72 percent of the cohort and all of the imaging for 12 percent. "A patient's cumulative risk of radiation-induced cancers is believed to increase with increasing cumulative radiation dose," Sodickson said. "The level of risk is further increased for patients scanned at young ages and is in general greater for women than for men. There is no absolute threshold, however, and the potential risks of radiation induced cancer must be balanced against the expected clinical benefits of the CT scan for the patient's particular scenario."

"CT is a tremendously valuable clinical tool in a wide variety of settings and disease processes, and as a result CT utilization has grown rapidly in recent years. Continued attention will be needed to keep radiation risks in check through a combination of technological advances, optimized imaging techniques, appropriateness criteria and patient-specific risk/benefit assessments," he said.

Though only a small proportion (1.9 percent) of ED patients undergoing CT of the neck, chest, abdomen, or pelvis have high cumulative rates of multiple or repeat imaging, the authors concluded that this patient subgroup may have a heightened risk of developing cancer from cumulative CT radiation exposure.