CT Scans Raise Your Cancer Risk

The number of CT scans performed in the United States has increased dramatically since the 1980s, and that means an increased risk of cancer for patients caused by exposure to high doses of radiation, according to a new report.

A CT scan-an imaging method that uses X-rays to create cross-sectional pictures of the body-can have radiation doses 50 to 250 times greater than the dose of a conventional X-ray, the report's authors note. Today, more than 62 million CT scans a year are done in the United States, compared with 3 million in 1980.

"The radiation doses from CT scans have been clearly demonstrated to increase cancer risk," said David J. Brenner, PhD, director of the Columbia University Radiological Research Accelerator Facility. "On an individual basis, not a big individual risk, but a small risk applied to an increasingly large population spells trouble down the road," he added.

Radiation’s Link To Cancer

Cancers from radiation, except leukemia, take years to develop, Dr. Brenner said. "However, in a few decades, 1.5% to 2% of all cancers in the United States may be due to the radiation from CT scans being done now," he said.

It takes 20 to 50 years after exposure to radiation before the full legacy of that exposure becomes evident, said Eric J. Hall, PhD, DSC, director of the Center for Radiological Research at Columbia University College of Physicians and Surgeons. "It takes a long time before the solid cancers emerge," he said. "The leukemias may come up in the first decade, but the solid cancers take a long time."

CT Scans And Children

Some 4 million to 5 million CT scans are done on children each year, and children are more sensitive to radiation than adults, Dr. Hall added. "A CT scan of the abdomen in a child gives a risk of about one in a 1,000 of an induced cancer," he said.

Unnecessary CT Scans

One-third of all CT scans, about 20 million a year, are medically unnecessary, Dr. Brenner said. "Anyone presenting to an emergency room with a belly ache or chronic headache will automatically get a CT scan," he said. "Is this justified? Well, maybe not."

Dr. Brenner said many CT scans could be replaced by other tests that don't involve X-rays, with ultrasound being one example.

"We were astonished to find how many doctors, particularly emergency room physicians, really have no idea of the magnitude of the doses or the potential risks that are involved in CT scans," Dr. Hall said.

Dr. Brenner said the use of CT scans is growing. New uses include diagnosing lung cancer, virtual colonoscopy and whole-body scans. "Most of these have not been proven to have a benefit over the risk," Dr. Hall said.

Diminishing Risk From CT Scans

Drs. Brenner and Hall said they aren't saying that people should avoid CT scans when they are appropriate. "Clearly, in a patient that's symptomatic, a CT is a wonderful diagnostic tool," Hall said. "What we are pushing for is to limit the use of CT to situations where it really is needed."

Drs. Brenner and Hall suggested three ways to diminish the risk from CT scans. First, the radiation dose should be reduced and tailored to individual patients. Second, CT scans should not be used when other options that have no radiation risk, such as ultrasound or magnetic resonance imaging (MRI), are appropriate. And the third suggestion—reducing the number of CT scans prescribed.

Adopting these strategies could keep some 20 million adults and more than one million children from unnecessary radiation exposure each year, the researchers said.

Expert Commentary

G. Donald Frey, PhD a professor of radiology at the Medical University of South Carolina, said he agreed that too many unnecessary CT scans are probably being performed. But, for those who need such a scan, the benefit outweighs the risk, he said.

"We are concerned that many CTs are done inappropriately," Dr. Frey said. "The whole community should work together to reduce inappropriate scans, but it would be absolutely tragic if a patient who needed a CT failed to get one because of concerns of the radiation dose."

Also, newer CT scanners have the ability to adjust the dose of radiation, Dr. Frey said.

"When CT scans are done on modern equipment where the dose can be adjusted to individual patient size, and when they are done in facilities that are accredited, the actual doses are being reduced,” he said.