Kids with complex heart disease at higher risk of imaging-induced cancer

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While imaging technologies and medical procedures for treating cardiac conditions have improved, there are risks, particularly to the youngest patients. Researchers found that children with heart disease who have the most difficult treatment paths face the greatest long-term risks for cancer.

Published online June 9 in Circulation, the study followed seven cohorts of children ages six years or younger undergoing treatment for heart disease between 2005 and 2010. While the median effective dose was nearly three times the yearly recommended limit for adults undergoing scans, the median associated risk of cancer was .07 percent. The highest risk of exposure was attributable to the severity of illness, imaging techniques used and the number of patients who needed to undergo more radiation intensive procedures.

Researchers led by Jason N. Johnson, MD, MHS, at Duke University Medical Center in Durham, N.C., followed 337 pediatric patients over the course of the five-year study to determine exposure risks. What they found was that most patients received less radiation exposure than one would experience in an average year in the U.S: 72 percent of patients received a median annual effective dose of 0.09-0.29 mSv. The annual background exposure for an average person is less than 4 mSv. However, “LAR [lifetime attributable risk] for cancer exceeded 0.5% at the upper limits of exposure for 6 of 7 cohorts, with the notable exception of children after arterial switch operation,” they stated.

Eight percent of the cumulative effective dose was represented by conventional radiographic examinations (92 percent of total examinations), while cardiac catheterizations, at 1.5 percent of all examinations, contributed more than half of the total radiation exposure (60 percent). Risks increased with the pediatric patients’ complexity of disease, as often repeated imaging with high-exposure techniques was needed to ensure accurate treatment. However, the less complex heart disease patients did not need as much repeated and high-exposure imaging and had far less risks.

“Although children benefit from advanced imaging procedures for more accurate diagnosis and less-invasive treatment, radiation has potential health risks,” Johnson et al wrote. “Several studies have shown that for a given dose of radiation, children are 3 to 4 times more likely than adults to develop malignancies.”

Exposure risks are concerning, particularly in young girls. Developing thyroid and breast tissue are highly susceptible to mutation. “LAR of cancer per unit exposure was substantially greater in females (41/100 000 versus 22/100 000 per 1 mSv effective dose for females versus males, respectively), which primarily reflects increased breast and thyroid cancer risk,” they wrote.

Johnson et al added that the severity of heart disease should not overshadow safety concerns. "Shortened anticipated lifespan in these high-risk cohorts does not mitigate cancer mortality and morbidity risks, because these children have a significantly increased relative risk of cancer even within the first 10 years after exposure. These data are consistent with epidemiological data demonstrating that the relative risk of cancer is highest in the early years after exposure."