While physicians agree that computed tomography (CT) scans are a life-saving diagnostic tool, new research has sparked renewed concern over their safety. One study found disturbing variations in radiation doses among scans, while another estimated that the 72 million CT scans in 2007 could cause 29,000 future cancers.
James A. Brink, MD, chair of diagnostic radiology at Yale School of Medicine, says the new studies highlight concerns many doctors have had for years.
“We still don’t know definitely whether medical radiation associated with CT scanning may cause cancer,” says Brink. “However, we must practice in the best interests of our patients and presume that a link exists. As such, we must reduce CT scanning doses to levels that are as low as reasonably achievable, and use CT scanning only when other imaging tests won’t suffice.”
What can patients do?
Brink is at the forefront of a hot debate over CT scanning as chairman of The National Council for Radiation Protection’s committee to define appropriate radiation levels for medical imaging procedures, and co-chairman of a world-wide awareness campaign called “Image Wisely.”
He offers the following advice to patients:
- If your physician recommends a CT scan, be sure it is truly indicated, and that a magnetic resonance imaging (MRI), ultrasound or X-ray wouldn’t be sufficient.
- Make sure repetitive CT scans are medically necessary.
- If you must have a CT scan, seek out a facility that is accredited by the American College of Radiology, which requires careful monitoring and control of the radiation dose.
Studies challenge CT use
The CT scan is a quick, painless, non-invasive test used to identify everything from brain tumors to internal injuries after trauma. In 2007, 72 million CT scans were performed in the United States – up from 3 million in 1980.
Two new studies published in the Archives of Internal Medicine in December examined the risks of excessive scans. One, led by Amy Berrington de González of the National Cancer Institute, combined cancer risk projections with the frequency of CT scan use in the United States, and estimated that 29,000 future cancers would be caused by CT scans in 2007. While early efforts to control radiation exposure were focused primarily on children, this study highlighted particular concern for adults aged 35 to 54 years.
The second study, led by Rebecca Smith-Bindman, from University of California-San Francisco, researched variability in X-ray doses associated with CT scans at four San Francisco-area hospitals, and found that patients undergoing common scans to the chest, abdomen and pelvis may be exposed to up to four times as much radiation as estimated in earlier studies.
Choose alternative tests
“One reason for the variations in doses is that, if you look at any institution, you have a wide mix of CT scanner types,” says Brink. “There are older scanners and newer scanners, and the older ones don’t have as many ways of adjusting the dose. Using the latest technology, we’re able to reduce the dose by an order of magnitude.”
Brink says physicians should order alternative imaging tests, such as ultrasound or MRI, for patients whenever possible. “I think that’s where we need to focus our attention,” he says, adding that some say that use of CT scans could be cut by as much as 30 percent.
“At Yale, radiologists have been examining and re-examining all of our dose reduction strategies,” says Brink. Initiatives have included use of the latest technical advances for dose reduction, and triaging patients to distinguish those who need a full dose CT scan from those who could benefit from a reduced dose CT scan, or alternative tests.
Yale radiologists have been using one alternative called MR enterography for patients with Crohn’s disease. As magnetic resonance imaging has improved, it has become highly accurate at capturing pictures of the bowel, says diagnostic radiologist Saravanan Krishnamoorthy, M.D. Crohn’s disease typically affects young people, and MRI is safe enough that doctors can perform multiple scans to track the disease throughout their lives, he says.
CT scans still best in some cases
Meanwhile, one thing that gets lost in the debate about CT scans is that the risk to any particular individual is very low, particularly as patients get older, Brink says. “CT will never go away, partly because there are certain parts of the body that are better imaged by CT – one of them is the lungs,” he says. “If CT scanning is needed medically, individuals should not shy away from having the test, as the risk of a fatal cancer from the associated radiation exposure (1 in 2,000 to 4,000) is very low as compared to the lifetime risk of developing a fatal cancer (1 in 4 or 5).”