CT radiation dose shows wide variance in ED

Despite growing concern over CT-related radiation exposure, measuring cumulative exposure from CT imaging in a standardized or formal way is not part of routine practice for ordering physicians in the emergency department, according to a presentation this week at the 2009 RSNA meeting.

"The use of CT in the U.S. has gone from three million CT scans performed annually in 1980 to more than 60 million in 2005," said Dr. Amita Kamath. "Little research has been done on quantifying cumulative exposure to CT, as well as associated radiation dose over time."

Kamath conducted a retrospective study at the University of California, San Francisco, of emergency patients who received a CT exam between October 2006 and March 2007. She and fellow author Dr. Rebecca Smith-Bindman assessed the cumulative use of CT within one year of a patient's ED visit, stratified by the reason for that patient's visit.

Their main outcome measures included the receipt of CT, receipt of repeated CT (defined as three or more CT exams within one year), and high radiation exposure (defined as a dose greater than 50 mSv).

The researchers identified the following groups from a cohort of 10,382 patients:

• trauma (3974 patients);
• altered mental status (3067 patients);
• renal stone disease (91 patients); and
• pancreatitis (61 patients).

Overall, 28% of patients received at least one CT scan. This ranged from approximately 20% to 22% of patients with trauma and altered mental status to 85% of patients with renal stone disease and 70% of patients with pancreatitis, Kamath said.

"Among patients who underwent CT imaging, the mean number of CT exams performed over the one-year period was two and varied from 1.8 in patients with trauma and altered mental status to 1.4 in patients with renal stone disease and 2.7 in patients with pancreatitis," she said.

The investigators found that 4% of patients received radiation exposure in excess of 50 mSv, with renal stone disease and pancreatitis patients most likely to receive this high dose, Kamath said.

"There is a statistically significant increase in cancer at effective doses in excess of 50 mSv," she said.

The research partners uncovered some disturbing trends in their analysis. In comparison with an altered mental status patient, a patient with renal stone disease was approximately 60 times more likely to receive a CT scan. Compared with patients with altered mental status, patients with pancreatitis were 20 times more likely-and patients with renal stone disease were eight times more likely-to receive a radiation dose of more than 50 mSv during the one-year study period.

"Use of imaging with CT is variable in the ED," Kamath said. "Several nonemergent diagnoses, such as renal stone disease and pancreatitis, were associated with the greatest increase in likelihood of receiving a CT, undergoing repeat CTs, and receiving a high radiation dose. For patients who undergo repeat CTs, a discussion between the ordering physician and radiologist is imperative to ensure that the most appropriate study is performed. This is particularly important given that many of these patients receive multiphase abdominal CT protocols, which average 30 mSv per scan."