Many patients going in for an abdominal CT scan get additional series largely intended only for patients with kidney problems, according to a study presented at the Radiological Society of North America (RSNA) on Monday.

Researchers at the University of Wisconsin in Madison examined almost 1,000 CT series from around 500 patients who had gone in for abdominal or pelvic CT scans in health centers or hospitals surrounding the university. They found that according to the American College of Radiology's Appropriateness Criteria, the industry standard for determining whether a scan is indicated, around a third of the scans (36 percent) in about half the patients (53 percent) were unnecessary, needlessly exposing the affected 263 patients to an excess dose of 20 millisieverts (mSv), or around 11 mSv if averaged out among all 500 participants. That average excess dose equals about 110 chest X-rays or three years of background radiation, according to the researchers.

Looking at the phases
"Radiology has come a really long way in terms of bringing [exposure] down," Kristie Guite, M.D., a radiology resident at Madison and lead author of the study, tells DOTmed News. "They always focus on optimizing the CT scanner itself, but nobody's really talked about looking at all these different phases," or additional imaging series.

In the study, Dr. Guite and her colleagues found that the biggest culprit for unindicated series was delayed-phase imaging, accounting for almost 78 percent of all unindicated exams.

Delayed-phase imaging, a technique that involves capturing images after injection of a contrast agent, is really only appropriate for patients with suspected kidney problems, according to Dr. Guite. "Many of the [doctors] we saw were doing delayed phases on everybody, and that seemed inappropriate to us, unless you're looking at a tumor in the kidney or something wrong with the kidneys," says Dr. Guite.

"A lot of our patients [examined] had follow-up exams for cancer," she continues. "So people who had prostate cancer, they had a delayed-phase, or people with some sort of abnormality in the liver. It's not appropriate then to do a scan in the kidneys," she adds.

And why were the doctors ordering excess exams? "We don't know," she admits. "We can speculate all we want, but the truth of the matter is we just don't know."

However, she does suggest that the rise of "defensive medicine" might have something to do with it. "People are doing catchall, one-size-fits-all sorts of approaches so as not to miss something."

Interestingly, fraud didn't seem to be responsible for the excess imaging, at least not with most of the patients in the study. Dr. Guite says she checked the rates of Medicare reimbursement for the procedures, and Medicare won't pay for additional intravenous contrast scans, such as the delayed-phase one.

The only area where there appeared to be real potential for abuse were non-contrast scans, she says. "Unfortunately, there were only 41 out of 500 patients that could have been billed unnecessarily," she adds. But because of the low numbers, she says it's "hard to extrapolate from that."

As for recommendations to patients, she says that while one CT scan is fine, patients should always ask their doctors if there's a way to get the same information with something that gives a lower - or no - radiation dose. "And when you start to have more than one scan," she says, "ask the technician how many phases will be performed. You can always talk to the radiologists to find out how much radiation you're getting...and what alternatives exist."

And as for Dr. Guite, she hopes that, after presenting the study at RSNA, to have it finished to submit to a journal some time in the beginning of next year.

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