Women Exposed To Low-Dose Radiation After MI At Greater Cancer Risk

Women who are exposed to low-dose ionizing radiation from cardiac imaging after myocardial infarction (MI) were found to be at greater risk for developing incident cancer compared with men, according to the results of a study published recently in the American Journal of Cardiology.

However, Patrick R. Lawler, MD, of McGill University Health Center, Montreal, Quebec, and colleagues emphasized in their discussion of the results that the low-dose radiation exposure that occurs after MI occurs during procedures with known benefit to the patient.

“Indeed, the benefits of many medical procedures likely outweigh the potential risks, and clinicians should be very wary of deferring useful interventions for the fear of low-dose ionizing radiation risk, doing so only when procedures are truly unnecessary or when alternative non-low-dose-ionizing-radiation-emitting technology is available,” they wrote.

Because prior research has shown that women are at an increased risk for malignancy compared with men after a similar amount of radiation exposure, Lawler and colleagues sought to determine if women had a greater risk for malignancy during low-dose ionizing radiation from cardiac imaging after MI.

They conducted a population-based longitudinal cohort study of all patients with a MI in Quebec between January 1996 and March 2006. The study included 82,861 patients; 68 percent were men and 32 percent were women.

Results showed that women had significantly less radiation exposure in the first year after MI than men, but no differences were found across varying age groups. After excluding cancers that were unrelated to radiation exposure, 6,934 new cancers were diagnosed with a median time to cancer diagnosis of 5.6 years after MI.

“We found, similarly to previous non-medical low-dose ionizing radiation cohorts, that women were at greater [relative risk] of developing a subsequent malignancy compared with men after similar exposure to low-dose ionizing radiation,” the researchers wrote.

For each millisievert of cardiac low-dose ionizing radiation exposure, women were at an increased risk for developing a cancer (HR=1.005; 95 percent CI, 1.002-1.008) compared with men with similar exposure (HR=1.002; 95 percent CI, 1.001-1.004). This result was after the researchers adjusted for age, non-cardiac radiation exposure, and other covariates.

In contrast, age was not an independent predictor of increased risk for cancer. 

The researchers said that there were several limitations to their study, including the possibility of residual confounders and the inability to include individualized measurement of radiation doses for each patient.

“These results support the hypothesis that medical sources of LDIR affect malignancy risk,” the researchers wrote. “It must be emphasized, however, that these are small [relative risks] and that the absolute risk difference on a population level would be expected to be very small.”