- One in 10 childhood blood cancers may result from medical imaging-associated radiation exposure.
- Cancer risk increased with cumulative radiation dose, ranging from 1.41 times higher to 3.59 times higher.
- Children exposed to at least 30 mGy had 25.6 excess blood cancers per 10,000 by age 21.
One of every 10 blood cancers in children may result from radiation exposure associated with medical imaging, according to a large retrospective analysis.
The risk of hematologic malignancy increased with cumulative radiation exposure versus none, ranging from 1.41 times higher for radiation doses of 1 to <5 mGy to 3.59 times higher for doses of 50 to <100 mGy. Cumulative radiation dose to bone marrow increased the risk of all hematologic cancers, reaching an excess relative risk of 2.54 per 100 mGy exposure. Other types of cancers also increased with imaging-associated radiation exposure.
For those exposed to at least 30 mGy of radiation, the excess cumulative incidence of hematologic cancers by age 21 was 25.6 per 10,000, reported Rebecca Smith-Bindman, MD, of the University of California San Francisco, and co-authors in the New England Journal of Medicine.
A key takeaway from the analysis is to avoid unnecessary imaging in children.
"The increasing use of low-value imaging in children and excessive radiation doses in CT are well documented," the authors wrote. "Our estimates of population-attributable risk suggest that up to 10% of hematologic cancers might be prevented by reducing unnecessary radiation exposure through more judicious imaging and appropriate doses. Although avoiding unnecessary imaging is critical, medically indicated imaging should not be deferred, because that may result in missed or delayed diagnoses."
The U.S. has the world's highest per-capita rate of diagnostic imaging. Though essential for diagnosis and disease management, most types of imaging involve ionizing radiation, which is a known carcinogen, Smith-Bindman and team noted in their introduction. Multiple studies have shown a dose-response relationship between radiation exposure and cancer risk, with CT leading the way.
Children are particularly susceptible to radiation-associated cancer because of their higher radiosensitivity and longer life expectancy as compared with adults. The highest risk from radiation exposure is for hematologic malignancies, the authors said. Several studies have shown a 50% higher risk of hematologic cancers in children undergoing two or three CT scans versus one.
Research remains scant with respect to the risks in North America or to radiation exposure from radiography, fluoroscopy, angiography, or nuclear medicine. To investigate the issue, Smith-Bindman and colleagues analyzed data from the Risk of Pediatric and Adolescent Cancer Associated with Medical Imaging retrospective cohort study.
Data encompassed 3.7 million children born between 1996 and 2016 in six U.S. healthcare systems and in Ontario, Canada. They were followed until development of a malignancy or benign tumor, death, end of healthcare coverage, age 21, or Dec. 31, 2017. Mean follow-up was 10.1 years, representing 35.7 million person-years of follow-up.
The investigators documented 2,961 hematologic cancers during follow-up, primarily lymphoid cancers (79.3%) or myeloid cancers/acute leukemia (15.5%).
Average imaging-associated radiation exposure was 14.0 mGy overall, and 24.5 mGy among children who developed hematologic cancers. For context, the authors noted that a single CT scan of the head involves radiation exposure of 13.7 mGy.
The data showed a dose-dependent relationship between radiation exposure and cancer risk (as compared with no radiation exposure):
- 1 to <5 mGy: relative risk (RR) 1.41 (95% CI 1.11-1.78)
- 15 to <20 mGy: RR 1.82 (95% CI 1.33-2.43)
- 50 to <100 mGy: RR 3.59 (95% CI 2.22-5.44)
The risk of all hematologic cancers and most tumor subtypes increased with cumulative radiation dose to bone marrow. For hematologic cancers, the excess risk per 100 mGy radiation exposure was 2.54 (95% CI 1.70-3.51, P<0.001), and the risk was 1.76 for a cumulative radiation exposure of at least 30 mGy. Associations decreased with increasing time since radiation exposure, and were stronger in children exposed at 5 years of age or older.
Excluding children with Down syndrome, cumulative exposure of at least 30 mGy was associated with a cumulative incidence of hematologic cancers of 39.9 per 10,000 children versus 14.3 for children with no exposure, resulting in 25.6 excess cancers per 10,000 children. The cumulative incidence increased to 55.1 per 10,000 for cumulative radiation exposure of 50 to 100 mGy, or 40.8 excess cancers per 10,000 children.
Calculations for population-attributable risk of hematologic cancers in children and adolescents showed that 10.1% of the cancers resulted from imaging-associated radiation exposure.
Disclosures
The study was supported by the National Cancer Institute, the Ontario Ministry of Health and Long-Term Care, and multiple other governmental organizations and agencies.
Smith-Bindman disclosed a relationship with Alara Imaging.
One co-author disclosed a relationship with Bayer.
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