CHICAGO--A large percentage of patients who undergo abdominal/pelvic CT receive unnecessary additional imaging series—along with avoidable radiation exposure—according to a study presented Monday at the annual meeting of the Radiological Society of NorthAmerica (RSNA).
"Radiation exposure has been a hot topic, particularly focusing on unnecessary radiation and over-exposure in patients during CT exams,” said Kristie Guite, MD, a radiation resident at the University of Wisconsin (UW) in Madison, and one of the authors of the study. “I think the recent events at Cedars-Sinai [in Los Angeles] reminds us that we are not doing every thing we can to minimize radiation exposure to patients.”
At Cedars-Sinai, patients undergoing brain perfusion CT scans were over-exposed by as much as eight-times the normal radiation exposure.
The researchers at UW-Madison reviewed the appropriateness and radiation dose of abdomen and pelvis CT exams for 500 patients performed at outside institutions and submitted to UW-Madison for interpretation. The patients ranged from the age of 9 months to 91 years, with most patients between the ages of 30 and 50.
A total of 978 imaging series were performed on the patients. The researchers, using the American College of Radiology Appropriateness Criteria, found that 345 of those CT series (35.3 percent) in 261 of the patients were not indicated. According to the researchers, the most common unnecessary exam was delayed-phase imaging (through which several images of the same part of the body are taken within a short period of time after a contrast injection in order to detect changes). This accounted for 268 of the 345 unnecessary exams.
“If we could eliminate these unindicated phases we could reduce overall radiation dose by 63 percent,” said Guite.
Guite pointed to the case of a 56-year-old patient as an example of the use of a multi-phase CT exam and inappropriate imaging. “He had a CT exam to follow up a pancreatic pseudocyst,” she explained. “Five phases were performed for that examination. The American College of Radiology Appropriateness Criteria recommends, at a maximum, three phases be performed. And at our institution, since this is a follow-up examination, we would only perform one of these phases. So this patient received almost 30 mSv of unnecessary radiation from the two excess series.”
Guite concluded that the “most important finding of this study is that adherence to ALARA (the radiation safety principle “As Low as Reasonably Achievable”) does not appear to be widespread at this time.”
Co-author J. Louis Hinshaw, MD, assistant professor radiology at UW-Madison, said that delayed-phase imaging is really only indicated in two situations—after trauma to evaluate the urinary system and to evaluate and characterize renal masses. “But most patients don’t have either one of these indications,” he said. “The point is that people are doing this despite the fact there is no good indication for it. Delayed-phase imaging should be very uncommon actually.”
So why is it being used when it isn’t indicated? “I suspect the reasons are two-fold,” Hinshaw said. “We have the tools and the ability to do it, and certainly that is sometimes abused.”
The other reason, he suggested, is that CT protocols are often “set up behind the scenes. They are set up to answer a question, but also to answer a ‘what if’ question. What if we see something in the liver, would it be helpful to have these additional phases? Certainly it would be, but our opinion is that the protocol should be set up to do the minimum amount of imaging.”