The ability to peer inside the body via medical imaging scans is nothing short of miraculous and has saved countless lives since X-rays were discovered 120 years ago. But experts have become increasingly concerned about the overuse of many types of scans in the U.S., not only because of the huge and growing expense and the risk of overdiagnosis, but also because of the potential cancer risk from the radiation they emit.
To CT or not to CT?
Of all imaging technologies commonly used today, CT (computed tomography) scans are the biggest source of radiation overall. Each year about 10 percent of Americans undergo CT imaging, sometimes multiple times, totaling more than 80 million scans. On average, we are exposed to at least six times more radiation from medical imaging (mostly CT) than we were three decades ago.
A special type of X-ray imaging test that produces cross-sectional images, or “slices,” of the body, CT scans are used to diagnose everything from heart disease and cancer to brain tumors, kidney stones, and injuries as well as to guide and monitor medical treatment. CT scans of the abdomen and pelvis tend to produce the most radiation, averaging 100 to 200 times more than a simple chest X-ray, 1,500 times more than dental X-rays, and 200,000 times more than airport scanners, though numbers vary widely.
Another way to look at it: The radiation from an average abdominal CT scan is comparable to three years of the natural “background” radiation (from soil, rocks, air, water, and the cosmos) the average person is exposed to in the U.S. Some newer uses for CT scans require even higher doses of radiation.
Other types of imaging that utilize relatively high levels of radiation include nuclear diagnostic tests, such as PET scans, as well as fluoroscopy (used for some cardiac and gastrointestinal diagnostic testing, among other things). In contrast, mammograms use relatively low doses of radiation—equal to about four chest X-rays—and contribute less than 1 percent of total radiation from medical imaging, according to a paper in the Journal of the American Medical Association in 2009. MRIs and ultrasound do not use any radiation at all.
Gauging the risk
High-energy radiation causes cancer by promoting DNA mutations and other cellular damage. The risk from a single CT scan may be minuscule, but radiation exposure is cumulative over a lifetime. Moreover, the potential risk across the population from all these millions of scans is substantial.
For instance, according to a widely cited study in the JAMA Internal Medicine in 2009, CT scans done in just one year (2007) in the U.S. were projected to cause an estimated 29,000 extra cases of cancer and eventually 14,500 deaths (scans done following a diagnosis of cancer and those performed during the last five years of a person’s life were excluded). That would be equal to about 2 percent of cancer cases diagnosed in the U.S. each year, from CT scans alone. At special risk for radiation exposure are health care professionals who work with the machines, at least if they don’t take all the proper protective measures.
While experts debate about both the basis for these estimates and their magnitude, everyone agrees that it makes sense to avoid unnecessary scans and reduce excessive radiation levels, especially in children. It’s believed that as many as one-third to one-half of all scans may be medically unnecessary. The hard part is to define “unnecessary” and to minimize the risks when testing is appropriate.
Little oversight, big variations
There are no federal standards on radiation doses from medical scans, except for mammograms. What’s more, there are no federal standards for training the technologists who use the highly complex imaging machines, which often differ in how they are operated.
Studies have shown that radiation doses from CT scans tend to be higher than the amounts generally cited. For a given procedure, the radiation dose can vary by as much as 13-fold between different facilities and even within the same facility, according to research by Rebecca Smith-Bindman, MD, and her colleagues at the University of California, San Francisco, published in the Archives of Internal Medicine. Dr. Smith-Bindman is one of the leading critics of misuse of CT scans. “Evidence suggests the radiation dose from CT scans could be reduced by 50 percent or more without reducing diagnostic accuracy,” she wrote in the New England Journal of Medicine in 2010.
What is being done to lower radiation exposures? New-generation CT scans can use much less radiation than older equipment, with no loss of image quality, and even newer “ultra-low dose” CT scans are being tested. Meanwhile, the FDA has undertaken a broad initiative to reduce unnecessary radiation exposure from medical imaging by, for instance, regulating the devices, recommending appropriate justifications for various procedures, and setting limits for optimal radiation doses. The nonprofit Joint Commission, which accredits health care organizations, now requires radiology departments to track dose levels used and to compare their data with those from other medical centers.
What to do
The American College of Radiology, the American College of Cardiology, andother expert groups advise that imaging tests be done only if there is a clear benefit that outweighs the risks—and that the minimal level of radiation be used.The only way to find out about this is to ask questions of your health care provider, such as the following:
- Is this test really necessary, and will it really improve my health care?
- Is there a nonradiation alternative, such as ultrasound or MRI, that’s equally good, and will insurance cover it? For instance, while CT scans are often used to diagnose kidney stones in emergency rooms, ultrasound is usually just as effective. Keep in mind that CT is better for certain things (such as broken bones, fractured vertebrae, cancer, pneumonia, bleeding in the brain, and trauma to organs such as the liver), while MRIs are better for others (such as brain tumors, most strokes, and injuries to tendons, ligaments, or the spinal cord); sometimes both are used. MRIs are more expensive.
- Is the facility accredited by the American College of Radiology? Are the CT technologists credentialed by the American Registry of Radiologic Technologists?
- Will the test use the lowest amount of radiation (adjusted for your body size) and fewest scans for adequate imaging? For children, who are at greatest risk, it’s important to make sure the radiation level is appropriate for their smaller size.
- Will the scan be limited to the indicated area, and will adjacent parts of your body be properly shielded?
- If the CT scan is a repeat of a previous one you’ve had, perhaps at a different facility, ask why it needs to be repeated. The Institute of Medicine reports that $8 billion is spent annually on repeat medical testing, much of that for scans and much of it unnecessary. Doctors often prefer to get a new test, especially if it will take time to get a copy of a previous scan. So let your doctor know if you recently had the same imaging test. Keep track of your scans, writing down the date, facility, and ordering doctor. Sometimes you can get copies of your scans put on a CD so you can show them to doctors.
Bottom line: Medical imaging tests are invaluable in the diagnosis and treatment of many disorders. You shouldn’t avoid necessary exams and procedures out of concern about radiation. And if a test doesn’t find anything, that doesn’t mean it was unnecessary. The best advice: Before having any imaging scan, discuss the pros and cons with your doctor.