Frequently used CT scans may raise cancer risk . 2 percent of future malignancies may be due to 'super X-rays,' study says

In a few decades, as many as 2 percent of all cancers in the United States might be due to radiation from CT scans given now, according to the authors of the report.

Some experts say that estimate is overly alarming. But they agree with the need to curb these tests particularly in children, who are more susceptible to radiation and more likely to develop cancer from it.

“There are some serious concerns about the methodology used,” but the authors “have brought to attention some real serious potential public health issues,” said Dr. Arl Van Moore, head of the American College of Radiology’s board of chancellors.

Doubled radiation exposure
The average American’s total radiation exposure has nearly doubled since 1980, largely because of CT scans. Medical radiation now accounts for more than half of the population’s total exposure; it used to be just one-sixth, and the top source was the normal background rate in the environment, from things like radon in soil and cosmic energy from the sun.

A previous study by the same scientists in 2001 led the federal Food and Drug Administration to recommend ways to limit scans and risks in children. But CT use continued to soar. About 62 million scans were done in the U.S. last year, up from 3 million in 1980. More than 4 million were in children.

Since previous studies suggest that a third of all diagnostic tests are unnecessary, that means that 20 million adults and more than 1 million children getting CT scans are needlessly being put at risk, Brenner and Hall write.

Ultrasound and MRI, or magnetic resonance imaging, scans often are safer options that do not expose people to radiation, they contend.

CT scans became popular because they offer a quick, relatively cheap and painless way to get 3D pictures so detailed they give an almost surgical view into the body. Doctors use them to evaluate trauma, belly pain, seizures, chronic headaches, kidney stones and other woes, especially in busy emergency rooms. In kids, they are used to diagnose or rule out appendicitis.

But they put out a lot of radiation. A CT scan of the chest involves 10 to 15 millisieverts (a measure of dose) versus 0.01 to 0.15 for a regular chest X-ray, 3 for a mammogram and a mere 0.005 for a dental X-ray.

As much radiation as atomic bomb survivors?
That puts them at risk of developing radiation-induced cancer, Brenner and Hall said. They base this on studies of thousands of Japanese atomic bomb survivors who had excess cancer risk after exposures of 50 to 150 millisieverts — the equivalent of several big CT scans.

Dr. Robert Smith, the American Cancer Society’s director of screening, said the authors’ estimate that 2 percent of future cancers may be due to CT scans “seems high.” But since cancers take 10 to 20 years to develop, “the ability to even observe that kind of an increase is going to be very difficult,” he said.

The authors stressed that they were not trying to scare people who need CT scans away from having them. In most cases, the benefits exceed the risks, especially for diagnostic scans.

However, using the scans to screen people with no symptoms of illness — like screening smokers for signs of lung cancer — has not been shown to save lives and is not currently recommended.