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Cancer risk found higher in women exposed to low-dose ionizing radiation than men
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Women exposed to low-dose ionizing radiation after an acute MI were more susceptible to cancer than men, according to new study data.
Patrick R. Lawler, MD, of McGill University Health Center and the Jewish General Hospital, Montreal, Quebec, and colleagues previously found a linkage between the low-dose ionizing radiation from cardiac imaging and therapeutic procedures and an increased risk for cancer. They sought to further this linkage by identifying the specific risks for women and younger patients.
The cohort consisted of 82,861 patients who had experienced an MI between 1996 and 2006. Sixty-eight percent (n=56,606) were men and 32% (n=26,255) were women. Exclusion criteria included any previous cancer diagnosis or comorbidity.
Researchers categorized patients according to age and levels of low-dose ionizing radiation. Men younger than 55 years had the highest mean exposure of 15.0 millisievert (mSv), whereas women 75 years or older had the lowest of 7.0 mSv. Overall, women had lower mean exposure than men (14.6 ± 14.4 mSv vs. 16.8 ± 14.4 mSv).
Adjusting for a 3-year lag between radiation exposure and cancer incidence, the researchers identified 6,934 cases of cancer during follow-up. The mean time between MI and cancer diagnosis was 5.6 years. The overall HR for cancer incidence per each mSv of low-dose ionizing radiation was 1.003 (95% CI, 1.002-1.005).
Lawler and colleagues found that cancer incidence increased with age, with an incidence of 0.6 per 100 person-years for patients younger than 45 years compared with an incidence of 3.08 for patients 65 to 74 years. However, age was not a predictor for cancer incidence based on units of mSv exposure (P=.93).
“Age has clearly been shown to be an important factor modulating malignancy risk associated with [low-dose radiation ionizing radiation] exposure,” the researchers wrote. “This risk asymptotically decreases in the first and second decades of life and remains relatively constant thereafter.”
Yearly cancer incidence was comparable between men and women (men, 2.12 vs. women, 1.96 per 100 person-years). However, after adjusting for age and noncardiac radiation, women were more likely to develop cancer for each mSv of exposure (HR=1.005; 95% CI, 1.002-1.008) than men (HR=1.002; 95% CI, 1.001-1.004; P=.014). Women were more likely to have cancer of the thorax, whereas hematologic cancer rates were higher in men.
The increased incidence of cancer found in women “may relate to relatively smaller body sizes for the same amount of radiation,” the researchers wrote.
Despite these findings, the researchers noted that the RRs for cancer incidence were small.
“We and others have shown that [low-dose radiation ionizing radiation] incurred after MI is primarily comprised of therapeutic procedures with known clinical benefit,” the researchers wrote. “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 radiation ionizing radiation] risk, doing so only when procedures are truly unnecessary or when alternative non-[low-dose radiation ionizing radiation]-emitting technology is available.”
Disclosure: The researchers report no relevant financial disclosures.
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