Multiple CT scans in kids triples cancer risk, but researchers caution overall risk low

(CBS/AP) Kids who get two or three CT scans before they turn 15 triple their risk of developing brain cancer, new research suggests.

The study also found kids who get five to 10 scans triple their risk for developing leukemia. However the researchers behind the new study say the absolute risk of developing cancer is still small and probably outweighed by the reason the child needs the CT scan in the first place. But study adds to a growing amount of research focusing on radiation risk for kids.

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The use of CT scans has risen rapidly since they were introduced 30 years ago. For children, they're used to evaluate head, neck or spine injuries or neurological disorders. Astudy last year found the number of kids who were given CT scans in an emergency room visit has risen five-fold between 1995 and 2008, from about 330,000 annual visits to 1.65 million.

For the study, published in the June 6 issue of The Lancet, international researchers studied nearly 180,000 patients under age 22 who had a CT scan in British hospitals between 1985 and 2002. The patients were tracked until 2008, and researchers found 74 of them were diagnosed with leukemia while 135 had brain tumors.

The scientists didn't measure the number of scans, which were mostly of the head, but examined data measuring radiation doses from the scans. That's because the amount of radiation received by body parts such as the brain and bone marrow depends on the age and size of the patient.

The children who later developed leukemia or brain tumors were compared to a group of people who got a very low dose of radiation to the same parts of their bodies.

"CT scans are very useful, but they also have relatively high doses of radiation, when compared to X-rays," said study author Dr. Mark Pearce, an epidemiologist at Newcastle University. He said CT scans were warranted in most situations but more needed to be done to reduce the amount of radiation.

Pearce emphasized these were rare diseases and that the higher risk was still small. The risk of leukemia in children is about 1 in 2,000, so having several CT scans would bump that up to about 1 in 600.

"What we definitely don't want is parents saying, 'No, I don't want my child to have a CT scan,' when he absolutely needs it," Pearce told TIME. "Although there is a tripling of risk, we are talking about a tripling of something small, and three times something small is still something small," he said. "We just need to look into making sure the scans are justified."

The researchers noted that modern CT scanners give off about 80 percent less radiation than the older machines used in the study. Even at low doses, the radiation can damage genes that may increase the patient's risk of developing cancer later.

The study was paid for by the U.S. National Cancer Institute and the U.K. Department of Health.

In the U.K., laws already require radiation from medical scans be kept as low as possible. In the U.S., the Food and Drug Administration is pushing manufacturers to design new scanners to minimize radiation exposure for the youngest patients, HealthPopreported last month. The agency also posted advice on the Internet urging parents to speak up when a doctor orders a scan - to ask if it's the best option or if there's a radiation-free alternative - and to keep a list of their child's medical scans that they should pull out every time a doctor considers ordering one.

A study last year found doctors may be too quick to prescribe a CT scan to rule out a traumatic brain injury for kids who hurt their heads, HealthPopreported, when taking an extra few hours to observe the kids in the emergency room could provide doctors with the information they need to make a diagnosis.

The American College of Radiology warned that fears of radiation should not prevent parents from getting necessary scans for their kids.

"If an imaging scan is warranted, the immediate benefits outweigh what is still a very small long-term risk," Dr. Marta Schulman, chair of the group's Radiology Pediatric Imaging Commission, said in a statement. "Parents should certainly discuss risk with their provider, but not refuse care that may save and extend their child's life."