Children with congenital heart disease exposed to low-dose ionizing radiation from cardiac procedures had a cancer risk more than triple that of pediatric congenital heart disease (CHD) patients without such exposures, according to a large Canadian nested case-control study presented at the joint scientific sessions of the American College of Cardiology and the World Heart Federation. The meeting was conducted online after its cancellation because of the COVID-19 pandemic.
This cancer risk was dose dependent. It rose stepwise with the number of cardiac procedures involving exposure to low-dose ionizing radiation (LDIR) and the total radiation dose. Moreover, roughly 80% of the cancers were of types known to be associated with radiation exposure in children, reported Elie Ganni, a medical student at McGill University, Montreal, working with MAUDE, the McGill Adult Unit for Congenital Heart Disease.
The MAUDE group previously published the first large, population-based study analyzing the association between LDIR from cardiac procedures and incident cancer in adults with CHD. The study, which included nearly 25,000 adult CHD patients aged 18-64 years with more than 250,000 person-years of follow-up, concluded that individuals with LDIR exposure from six or more cardiac procedures had a 140% greater cancer incidence than those with no or one exposure (Circulation. 2018 Mar 27;137[13]:1334-45).
Because children are considered to be more sensitive to the carcinogenic effects of LDIR than adults, the MAUDE group next did a similar study in a pediatric CHD population included in the Quebec Congenital Heart Disease Database. This nested case-control study included 232 children with CHD who were first diagnosed with cancer at a median age of 3.9 years and 8,160 pediatric CHD controls matched for gender and birth year. About 76% of cancers were diagnosed before age 7, 20% at ages 7-12 years, and the remaining 4% at ages 13-18. Hematologic malignancies accounted for 61% of the pediatric cancers, CNS cancers for another 12.5%, and thyroid cancers 6.6%; all three types of cancer are associated with radiation exposure.
After excluding all cardiac procedures involving LDIR performed within 6 months prior to cancer diagnosis, the risk of developing a pediatric cancer was 230% greater in children with LDIR exposure from cardiac procedures than in CHD patients without such exposure. For every 4 mSv in estimated LDIR exposure from cardiac procedures, the risk of cancer rose by 15.5%. In contrast, in the earlier study in adults with CHD, cancer risk climbed by 10% per 10 mSv. Patients with six or more LDIR cardiac procedures – not at all unusual in contemporary practice – were 2.4 times more likely to have cancer than those with no or one such radiation exposure.
Current ACC guidelines on radiation exposure from cardiac procedures recommend calculating an individual’s lifetime attributable cancer incidence and mortality risks, as well as adhering to the time-honored principle of ensuring that radiation exposure is as low as reasonably achievable without sacrificing quality of care.
“Our findings strongly support these ACC recommendations and moreover suggest that radiation surveillance for patients with congenital heart disease should be considered using radiation badges. Also, cancer surveillance guidelines should be considered for CHD patients exposed to LDIR,” Mr. Ganni said.
These suggestions for creation of patient radiation passports and cancer surveillance guidelines take on greater weight in light of two trends: the increasing life expectancy of children with CHD during the past 3 decades as a result of procedural advances that entail LDIR exposure, mostly for imaging, and the growing number of such procedures performed per patient earlier and earlier in life.
He and the MAUDE group plan to confirm their latest findings in other, larger data sets and hope to identify threshold effects for LDIR for specific cancers, with hematologic malignancies as the top priority.
Mr. Ganni reported having no financial conflicts regarding his study, funded by the Heart and Stroke Foundation of Canada, the Quebec Foundation for Health Research, and the Canadian Institutes for Health Research.