Unnecessary sequences add to radiation burden

Adding noncontrast and delayed-contrast series to abdominal/pelvic CT examinations appears common in routine clinical practice and represents a potential public health danger with no associated clinical benefit, according to a presentation Monday afternoon at the 2009 RSNA meeting.

"The recent events at Cedars-Sinai have reminded us that we are not doing everything we can to minimize radiation exposure," said Dr. Kristie Guite from the radiology department at the University of Wisconsin in Madison.

In October, the FDA and Cedars-Sinai Medical Center revealed that 206 stroke patients who received CT scans at the Los Angeles hospital were overdosed with radiation.

However, according to research Guite began as a medical student and has continued during her residency, the Cedars-Sinai experience with CT-based radiation overdose is not unique.

Guite has focused her attention on a potentially significant source of excess radiation that has not heretofore been examined: additional CT series (such as routine noncontrast or delayed-contrast scans) conducted during an exam that are not supported by the medical literature.

"Medical radiation exposure should be reduced to only that which is needed in order to make a diagnosis," she said.

Guite reviewed 500 abdomen and pelvis CT exams performed at outside institutions and submitted for tertiary interpretation for appropriateness (using the American College of Radiology criteria) and for radiation dose.

"Radiation dose was calculated using the ImPACT [London] CT dose calculator, and associated cancer risks were estimated using methods described in the Beir VII report," Guite said.

There were a total of 978 series for 500 patients. Guite noted that nonindicated multiphasic series were found in 52.2% of the exams, the most common being delayed phase imaging in 77.7% of them.

She reported that the mean total radiation dose per patient was 34 (± 24.1) mSv. The nonindicated series had a mean dose of 16.3 (± 9.4) mSv, which resulted in a mean excess dose of 11.3 mSv per patient for the entire study population.

According to Guite, using the linear-no-threshold model of radiation risk, these unnecessary CT sequences could be delivering a significant radiation burden to patients.

"Extrapolation of this dose over the total number of abdomen/pelvis CT scans performed each year in the U.S. would result in an excess lifetime attributable risk of 0.1% for those undergoing an abdomen/pelvis CT exam, or up to 23,000 radiation-induced cancer cases per year," she said.