X-rays are a wonderful diagnostic tool, but like many other tests, they come with risks. In this case, radiation, an excess of which can lead to cancer. CT scans, which create detailed images of the interior of the body, are superior for diagnosing several medical problems—more than 80 million are performed every year in the U.S.

But they use significantly more radiation than standard X-rays, and a breakthrough study in Britain confirms that the risk is higher for children.

Concern about the effects of radiation are especially appropriate for children, who are at greater risk because their cells turn over more rapidly and because they have a longer life span in which to be exposed to all forms of radiation. We’ve addressed this concern before, and have described the general risk in “Radiation Overdose Injuries.”

As reported by NPR in conjunction with Kaiser Health News, children who get CT scans have a slightly higher risk for brain cancer and leukemia, according to the study published in the Lancet.

The study is considered significant because it’s the first to follow youngsters who had CT scans for their subsequent cancer risk. Nearly 180,000 patients who got CT scans between 1985 and 2002 before their 22nd birthdays were followed.

Researchers calculated that the amount of radiation from two or three scans of the head before age 15 would increase the risk of brain cancer threefold. It would take five to 10 head scans to triple the risk of leukemia.

Researchers emphasized that the overall risk for brain cancer and leukemia is very low, so although a threefold increase sounds ominous, the risk remains quite low even among people who got scans.

In the 10 years following the scans, researchers estimated that about one excess brain tumor and one case of leukemia occurred per 10,000 head CT scans performed in young children.

But scans of other parts of the body also look risky, they concluded, and it's probably not just a matter of multiple CTs and leukemia and brain tumors among kids; there's a good chance even one CT scan poses some risk to children and possibly for various cancers.

Experts say it's important to remember that CT scans save a lot of lives, and that they are certainly appropriate in some situations, including:

• major motor vehicle accidents where there's multiple potential organ injuries;
• abdominal pain for which surgery might be required—for example a bowel obstruction or sometimes appendicitis;
• for some symptoms of head injuries, but not all.

The bottom line is that many CT scans are unnecessary, and doctors must be much more selective about how are used.

If your doctor suggests that you or your child has a CT scan, ask why. Ask if there are other options, such as ultrasound, which doesn’t offer as much detail as a CT scan, but in some cases is a sufficient diagnostic approach.