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Friday, Nov 30, 2007
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Growing radiation perils

How CT scans raise cancer risks

Risk of developing radiation-induced cancer
Need to curb the tests, particularly on children

NEW YORK: Millions of people, especially children, are needlessly getting dangerous radiation from “super X-rays” that raise the risk of cancer and are increasingly used to diagnose medical problems, a report warns.

In a few decades, as many as 2 per cent of all cancers in the U.S., for example, might be due to radiation from CT scans given now, according to the report’s authors.

Some experts say that estimate is overly alarming. But they agree with the need to curb these tests particularly on 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.

Built-up risk

The risk from a single CT, or computed tomography, scan to an individual is small. But “we are very concerned about the built-up public health risk over a long period of time,” said Eric J. Hall, who wrote the report with fellow Columbia University medical physicist David J. Brenner. It was published in Thursday’s New England Journal of Medicine and paid for by U.S. grants.

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.

Earlier study

A previous study by the same scientists in 2001 led the Food and Drug Administration to recommend ways to limit scans and risks in children. But CT use has continued to soar. In the U.S. alone, about 62 million scans were done last year, up from three million in 1980. More than four 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 a million children getting CT scans are needlessly being put at risk, Mr. Brenner and Mr. Hall write.

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

Detailed 3D pictures

CT scans became popular because they offer a quick, relatively cheap and painless way to get three-dimensional 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. The dose depends on the type of machine and the person — obese people require more radiation than slim ones — and the risk accumulates over a lifetime.

“Medical care in this country is naturally so fragmented. Any one doctor is not going to be aware of the fact that a particular patient has had three or four CT scans at some point in the past,” said Dr. Michael Lauer, prevention chief at the National Heart, Lung and Blood Institute.

People with chronic problems like kidney stones are likely to get too many scans, said Dr. Fred Mettler, radiology chief in the New Mexico Veterans Administration health care system. “I’ve seen people who are 30 years old who have had at least 18 scans done,” he said.

Comparison

That puts them at risk of developing radiation-induced cancer, Mr. Brenner and Mr. 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.

“That’s very controversial. There’s a large portion of the medical physics community that would disagree with that” comparison, said Richard Morin, a medical physicist at the Mayo Clinic in Jacksonville, Florida.

Others defended the data, which have been widely cited in other radiation studies. “It’s the best evidence we’ve got” on cancer risks, Dr. Lauer said. — AP

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