Children and teens often get diagnostic tests that expose them to radiation, increasing the risk of cancer later in life, U.S. researchers said on Monday.

“In just a three-year span, 42.5 percent of kids got some form of ionizing radiation from a diagnostic medical procedure,” said Dr. Adam Dorfman, a pediatric cardiologist at the University of Michigan in Ann Arbor, whose study appears in the Archives of Pediatrics and Adolescent Medicine.

The study is among the first to look at radiation exposure among children and teenagers, who have the biggest long-term cancer risk from early and repeated exposure to radiation.

Dorfman’s team studied health claims data on more than 355,000 children and teens under age 18 who were covered by UnitedHealth Group, a large U.S. health insurer.

They analyzed tests ranging from a simple X-ray to more advanced tests such as computed tomography or CT scans, which produce cross-sectional pictures of the body but deliver a much higher radiation dose.

A chest CT delivers more than 100 times the radiation dose of a typical chest X-ray.

“Nearly eight percent (7.9 percent) got at least one CT scan, and 3.5 percent got at least two CT scans in those three years,” Dorfman said in a telephone interview.

CT scans of the head were the most common.

Radiation exposure became a major concern in October 2009 after the U.S. Food and Drug Administration said it was investigating more than 2,000 cases in which patients received toxic doses of radiation during CT scans of the brain at a California hospital.

While several studies have focused on rates of adult exposure to radiation from imaging tests, few have looked at children. “It really seemed like there was a big hole in the data in kids,” Dorfman said.

In children, the biggest risk from radiation exposure is cancer, although almost any body system can be affected, Dorfman said.

The team looked at three years of claims data from children from Arizona, Dallas, Orlando, south Florida and Wisconsin.

The data did not show what the children were being tested for, but Dorfman said the study is important because it offers a benchmark for how many tests are being done in children.

“While I can’t say any given procedure was appropriate or inappropriate, I think as a whole we have to make sure when these studies are being used, they are used only when they are absolutely necessary,” he said.

Right now, he said there are few studies that can answer that question. “We need data on when they are necessary for clinical care,” Dorfman said.

The team plans to use the data in future studies to calculate radiation doses in children.

In November, the FDA asked several CT equipment makers - which include General Electric, Toshiba Corp, Hitachi Ltd, Siemens and Philips - to add safety features to their CT machines.

Many companies already offer special features to help reduce radiation dose in scans involving children.

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By Julie Steenhuysen

CHICAGO