June 6, 2012 -- Gina Baker carefully weighed the pros and cons of a CT scan for her 1-year-old son.
"His pediatrician said she wanted to do a scan to make sure everything was OK," said Baker, explaining concerns that "the little guy's" head was growing too quickly. "They told me the risks from the radiation were low, but you definitely struggle with those types of decisions as a parent."
The scan came back normal, giving Baker some peace of mind. But the 31-year-old nurse and blogger from Brigham City, Utah, said she still worries about the test's long term effects -- a fear bolstered by a new study linking childhood CT scans to cancer later in life.
"Radiation exposure from CT scans was associated with an increased risk of brain cancer and leukemia, and that risk increased with increasing levels of radiation exposure," said Amy Berrington de González, a radiation epidemiologist at the National Cancer Institute in Bethesda, Md., and co-author of the study published today in The Lancet.
The study, of more than 355,000 children and teens in the U.K., found those exposed to 60 milligrays of radiation -- the cumulative dose of two brain CT scans -- were three times more likely to develop brain tumors. Those exposed to 50 milligrays of radiation were three times more likely to develop leukemia, a cancer of the white blood cells produced in the bone marrow.
Berrington de González stressed that the absolute cancer risk is very small, accounting for one extra cancer case per 30,000 children scanned.
"Providing the scan is clinically justified and performed properly with a child size dose of radiation, the benefits should easily outweigh the risks," she said.
But for parents like Baker, forced to quickly weigh the immediate benefits with the long term risks, the decision is far from easy.
"You want to do what's best for your family," she said. "I did agonize over it."
Radiation has long been known to cause DNA damage that can lead to cancer. But the cancer-causing effects of doses doled out during CT scans were purely theoretical.
"Those estimates drew a lot of controversy because they were based on the cancer risk in atomic bomb survivors," said Dr. David Brenner, director of Columbia University's Center for Radiological Research and lead author of the 2001 study estimating the cancer risk from CT scans. "There was debate about whether the risks were real, and this study shows pretty unequivocally that they are."
But Brenner said the benefits of CT scans, namely their ability to quickly detect life-threatening problems and guide life-saving surgeries, indeed outweigh the risks.
"All medical procedures have risks and benefits," he said. "That said, there are situations where CT scans are being used too much."
Brenner estimates some 20 percent of the country's 80 million CT scans each year are either unnecessary or could be replaced by a radiation-free ultrasound or MRI.
"That's why we need basic guidelines; decision rules that determine when a CT scan is medically appropriate," he said, adding that such guidelines already exist but are not always used.
Dr. Andrew Einstein, director of cardiac CT research at Columbia University Medical Center in New York City and author of an editorial accompanying the study, said he hopes doctors to think twice before ordering CT scans in children and parents will ask about alternatives.
"I think we need to redouble our efforts to ensure patients are getting appropriate tests with the lowest radiation dose possible," he said. "There are good reasons to use CT scans; it's a lifesaving test for many people. But with every good thing in medicine, there's a potential downside. And for CT scans it's the radiation."