In the largest study of the effects of cumulative radiation doses on children with heart disease, researchers found that children who are exposed to repeated complex imaging tests have a slightly increased lifetime risk of cancer. Published in the June 9 journal Circulation, the study also found that low levels of radiation during X-rays do not carry an increased risk.
Children with heart disease frequently undergo imaging tests, including X-rays, CT scans and cardiac catheterization procedures that use video X-rays called fluoroscopies. The number of imaging studies patients are exposed to depends on the complexity of their disease, with more serious conditions typically requiring more testing.
“We know that each of these individual tests carries a small amount of risk, but for patients who get frequent studies as part of their care, we wanted to better understand the risk associated with repeated exposure,” said senior author Kevin D. Hill, MD, an interventional cardiologist and assistant professor of pediatrics at the Duke University Medical Center, Durham, N.C, in a news release.
To determine the risk of lifetime cancer from exposure to imaging procedures, researchers at Duke University Medical Center studied 337 children under the age of 6 who had surgery for heart disease from 2005 to 2010. Over the course of the five-year study, the children averaged 17 imaging tests each before and after their surgeries. Collectively, the children in the study underwent nearly 14,000 imaging procedures.
To assess the children’s exposure to radiation, Hill and his colleagues examined medical records to find out which imaging tests were most commonly used. To determine the amount of radiation delivered in the tests, the research team used a combination of existing data on radiation levels and simulations that calculated radiation doses using child-sized models to estimate radiation exposures.
Based on their findings, the investigators concluded that the average child in the study had a relatively low risk of cancer from standard X-rays. However, certain groups of children, especially those with more complex heart disease who required repeat CT scans or cardiac catheterizations, had a significantly higher lifetime risk of cancer.
The study revealed that abdominal and chest X-rays accounted for 92 percent of the imaging tests, but only 10 percent of radiation exposure. CT scans and catheterizations made up 8 percent of the imaging procedures, but accounted for 81 percent of radiation exposure.
In addition, the researchers found that girls had a greater cancer risk than boys. They indicated girls had double the risk because of their increased chances of developing breast cancer and thyroid cancer.
Overall, Hill and his team estimated the average increased risk in lifetime cancer from radiation exposure to be 0.07 percent. The risk from chest X-rays is 0.002 percent compared to 0.4 percent from complex imaging.
The study authors noted in the news release that “in general, the benefits of imaging far outweigh the risks of radiation exposure.” But Hill and his team also cautioned that steps need to be taken to minimize exposure to radiation.
“Clinicians need to weigh the risks and benefits of different imaging studies, including those with higher radiation exposure,” said Hill. “We’re not proposing eliminating complex imaging – in fact, they’re critically important to patients – but we can make significant improvements by prioritizing tests and simply recognizing the importance of reducing radiation exposure in children.”