In a study reported in The New England Journal of Medicine, Smith-Bindman et al found that medical imaging among children was associated with a significantly increased risk of pediatric and adolescent hematologic cancer.
The study involved data from a retrospective cohort of 3,724,623 children born between 1996 and 2016 in six U.S. health-care systems and Ontario, Canada. Follow-up was until the earliest of cancer or benign tumor diagnosis, death, end of health-care coverage, age 21 years, or the end of December 2017.
Key Findings
During 35,715,325 person-years of follow-up, a mean of 10.1 years per person, 2,961 hematologic cancers were diagnosed; of these cancers, the most common were lymphoid cancers (n = 2,349; 79.3%), myeloid cancers or acute leukemia (n = 460; 15.5%), and histiocytic or dendritic cell cancers (n = 129; 4.4%).
For reference, the exposure from one computed tomography scan of the head was 13.7 mGy. The mean exposure among all children exposed to at least 1 mGy was 14.0 ± 23.1 mGy; the mean exposure among children developing hematologic cancer was 24.5 ± 36.4 mGy.
Cancer risks increased with increased cumulative dose: relative risks vs no exposure were 1.41 (95% confidence interval [CI] = 1.11–1.78) for 1 to < 5 mGy, 1.82 (95% CI = 1.33–2.43) for 15 to < 20 mGy, and 3.59 (95% CI = 2.22–5.44) for 50 to < 100 mGy.
The cumulative radiation dose to bone marrow was associated with an increased risk of all hematologic cancers, with an excess relative risk per 100 mGy of 2.54 (95% CI = 1.70–3.51, P <.001) and a relative risk for 30 vs 0 mGy of 1.76 (95% CI = 1.51–2.05). The excess cumulative incidence of hematologic cancers by age 21 years among children exposed to at least 30 mGy (mean = 57 mGy) was 25.6/10,000 population.
It was estimated that 10.1% (95% CI = 5.8%–14.2%) of hematologic cancers in the study cohort could be attributed to radiation exposure from medical imaging. Higher risks appeared to be associated with exposure to higher-dose medical imaging, such as computed tomography.
The investigators concluded: “Our study suggests an association between exposure to radiation from medical imaging and a small but significantly increased risk of hematologic cancer among children and adolescents.”
Rebecca Smith-Bindman, MD, of the Department of Epidemiology and Biostatistics, University of California, San Francisco, is the corresponding author of The New England Journal of Medicine article.
Disclosure: The study was funded by the National Cancer Institute and others. For full disclosures of all study authors, visit nejm.org.
