Advanced heart imaging raises lifetime cancer risk of children

Children with heart disease are exposed to low levels of radiation during X-rays, which do not significantly raise their lifetime cancer risk. However, children who undergo repeated complex imaging tests that deliver higher doses of radiation may have a slightly increased lifetime risk of cancer, according to new research.

The findings, from Duke Medicine in Durham, North Carolina and published in the journal Circulation (2014; doi:10.1161/CIRCULATIONAHA.113.005425), represent the largest study of cumulative radiation doses in children with heart disease and associated predictions of lifetime cancer risk.

Children with heart disease frequently undergo imaging tests, including X-rays, computed tomography (CT) scans and cardiac catheterization procedures. The number of imaging studies that patients are exposed to depends on the complexity of their disease, with more serious heart conditions typically requiring more testing. Advanced imaging procedures offer the benefits of more accurate diagnosis and less invasive treatment, but the increase in radiation has potential health risks.

"In general, the benefits of imaging far outweigh the risks of radiation exposure, which on a per study basis are low," said senior author Kevin D. Hill, MD, MS, an interventional cardiologist and assistant professor of pediatrics at Duke University School of Medicine.

"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 Hill.

Hill and his colleagues studied a group of 337 children ages six years and younger who had one or more surgeries for heart disease from 2005 to 2010. During the five-year study period, each of the children received an average of 17 imaging tests as part of their medical care before and after their surgeries.

The researchers found that most children had low exposure to radiation, amounting to less than the annual background exposure in the United States. However, certain groups of children, particularly those with more complex heart disease, were exposed to higher cumulative doses from repeated tests and high-exposure imaging.

Abdominal and chest X-rays accounted for 92% of the imaging tests, but only 19% of the radiation exposure. Advanced imaging (CT and catheterization) made up only 8% of imaging tests performed, but accounted for 81% of radiation exposure.

The researchers estimated the average increase in lifetime cancer risk to be 0.07%, with the risk increase ranging from 0.002% for chest X-rays to 0.4% for complex imaging.

"Clinicians need to weigh the risks and benefits of different imaging studies, including those with higher radiation exposure," Hill said. "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."

The researchers also noted that lifetime cancer risk was increased among girls and children who had imaging tests done at very young ages. Girls had double the cancer risk of boys because of their increased chances of developing breast and thyroid cancers.

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