Exposure to radiation from medical imaging is linked to a small but significant increased risk of blood cancers among children and adolescents, according to a study published September 17 in the New England Journal of Medicine.
The finding is from a retrospective analysis involving more than 3.7 million children born in the U.S. or Ontario, Canada, with researchers suggesting medical imaging was associated with 10.1% of hematologic cancers.
“This study provides robust, directly observed evidence that ionizing radiation from medical imaging was associated with an increased risk of hematologic cancer among children, even at doses of less than 50 mGy,” noted first author Rebecca Smith-Bindman, MD, of the University of California, San Francisco, and colleagues.
International studies have linked childhood CT to increased risk of hematologic cancers, showing a 50% higher risk among children undergoing two or three CT scans than among those undergoing one scan, according to the authors. Yet research is lacking with respect to these risks in North America or with respect to radiation exposure from radiography, fluoroscopy, angiography, or nuclear medicine, they noted.
To bridge the knowledge gap, the group analyzed results from the Risk of Pediatric and Adolescent Cancer Associated with Medical Imaging (RIC) study, which followed more than 3.7 million children born between 1996 and 2016 in any of six integrated U.S. health care systems or Ontario, Canada. Children were tracked until the earlier cancer diagnosis, death, end of healthcare coverage, or age 21.
The researchers quantified radiation doses to active bone marrow from imaging and estimated associations between hematologic cancers and cumulative radiation exposure (versus no exposure), with a lag of six months, with continuous-time hazards models.
During a mean follow-up of 10.1 years per person, 2,961 hematologic cancers were diagnosed, primarily lymphoid cancers (2,349 [79.3%]), myeloid cancers or acute leukemia (460 [15.5%]), and histiocytic- or dendritic-cell cancers (129 [4.4%]), the authors reported.
The mean exposure among children exposed to at least 1 mGy was 14.0 ± 23.1 mGy overall and 24.5±36.4 mGy among children with hematologic cancer. For comparison, 13.7 mGy was the exposure from one CT scan of the head, the group wrote. In addition, according to calculations, a 15-to-30-mGy exposure equivalent to one to two CT scans of the head was associated with an increased risk by a factor of 1.8, rising to a factor of 3.6 for exposures of 50 to less than 100 mGy.
The excess cumulative incidence of hematologic cancers by 21 years of age was 25.6 per 10,000 among children exposed to at least 30 mGy and 40.8 per 10,000 among those exposed to 50 to 100 mGy, the group reported.
The researchers noted that attributable risks varied according to imaging type. For instance, among children who underwent CT of the head, a quarter of hematologic cancers were estimated to be attributable to radiation exposure, whereas among children undergoing radiography, such as for a broken bone or pneumonia, a very small percentage (<1%) of hematologic cancers were estimated to be associated with radiation exposure.
“We estimated that, in our cohort, 10.1% (95% CI, 5.8 to 14.2) of hematologic cancers may have been attributable to radiation exposure from medical imaging, with higher risks from the higher-dose medical-imaging tests such as CT,” the group wrote.
Ultimately, the study adds to the growing evidence that associates pediatric medical imaging with cancer risk and addresses key limitations of previous studies, the group wrote.
“Although CT and other radiation-based imaging techniques may be lifesaving, our findings underscore the importance of carefully considering and minimizing radiation exposure during pediatric imaging to protect children’s long-term health,” the researchers concluded.
A longtime advocate for lowering radiation dose levels in medical imaging, Smith-Bindman also recently led research that estimated that cancers associated with radiation from CT scans could eventually account for 5% of all new cases annually. That study elicited a response from the American Association of Physicists in Medicine.
In addition, UCSF researchers developed a CT quality measure for the U.S. Centers for Medicare and Medicaid Services (CMS). In 2014, Smith-Bindman co-authored an op-ed in the New York Times, linking the overuse of CT to rising cancer rates and even death in patients who are scanned.
In an accompanying editorial, Lindsay Morton, PhD, of the National Cancer Institute in Bethesda, MD, said the results of this study expand understanding of health risks associated with low-dose (<100 mGy) radiation exposure.
While the results should be “reassuring to individual patients,” the report “further raises the specter of radiation-related hematologic cancer risks beyond acute lymphoblastic leukemia and acute myeloid leukemia to other subtypes, such as non-Hodgkin’s lymphoma,” Morton wrote.
Long-term strategic support of radiation-related research and education should remain a high priority, Morton added. However, in the short term, campaigns such as Image Wisely and Image Gently provide helpful information to guide decision-making, she noted.
Read the complete paper here.