UPDATED Sept 24, 2025 // Editor's note: This story was updated with additional context from an editorial.

TOPLINE:

Radiation exposure from medical imaging was associated with a 3.59-fold increased risk for hematologic cancer in children receiving 50 to < 100 milligray (mGy) compared to those who had no exposure. Researchers estimate that 10.1% of hematologic cancers may be attributable to medical imaging radiation exposure.

METHODOLOGY:

• Ionizing radiation-based imaging is known to increase the risk for cancer, but the extent of risk associated with low-dose radiation exposure has been unclear.
• A retrospective cohort study followed 3,724,623 children born between 1996 and 2016 in six US healthcare systems and Ontario, Canada, until cancer diagnosis, death, end of coverage, age 21, or December 2017.
• Researchers quantified radiation doses to active bone marrow from medical imaging and analyzed associations between hematologic cancers and cumulative radiation exposure using continuous-time hazards models.
• Analysis included a 6-month lag period between exposure and outcome assessment to evaluate cancer risk, with sensitivity analyses using a 24-month lag period.
• Investigators examined multiple cancer subtypes including lymphoid cancers (79.3%), myeloid cancers or acute leukemia (15.5%), and histiocytic or dendritic cell cancers (4.4%).

TAKEAWAY:

• Cancer risk increased with cumulative dose, showing (relative risk [RR], 1.41; 95% CI, 1.11-1.78) for 1 to < 5 mGy (RR, 5.64; 95% CI, 2.80-9.92) and for at least 100 mGy compared to no exposure.
• The excess relative risk per 100 mGy (RR, 2.54; 95% CI, 1.70-3.51; P < .001) was for all hematologic cancers (RR for 30 mGy vs 0 mGy, 1.76; 95% CI, 1.51-2.05).
• Among children without Down syndrome, the cumulative incidence of hematologic cancer by age 21 was 39.9 per 10,000 for those exposed to radiation ≥ 30 mGy compared to 14.3 per 10,000 for children who were unexposed.
• CT of the head was linked to a mean radiation exposure of 13.7 ± 8.0 mGy (RR, 1.35; 95% CI, 1.23-1.48) and an attributable risk of 25.9%.

IN PRACTICE:

“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. Furthermore, our results quantify the risk of cancer associated with medical imaging through 21 years of age, but cumulative incidence will probably increase with longer follow-up,” the authors of the study wrote.

According to an accompanying editorial, the findings expand understanding of health risks associated with low-dose (< 100 mGy) radiation exposure, “which can inform radiation-protection standards and radiation-related carcinogenesis.” 

“The report by Smith-Bindman et al is an important addition to the growing body of direct evidence regarding the small risks of cancer after low-dose radiation exposure. It also confirms the relatively short latency (interval between exposure and cancer diagnosis) of radiation-related hematologic cancers as compared with solid tumors and 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,” the author of the editorial wrote.

SOURCE:

The study was led by Rebecca Smith-Bindman, MD, Department of Epidemiology and Biostatistics, University of California San Francisco. It was published online on September 17 in The New England Journal of Medicine.

LIMITATIONS:

According to the authors, potential under-ascertainment of cancers was a limitation, though this was minimized by linking with population-based tumor registries. The study’s follow-up period ended at age 21, suggesting that cumulative cancer incidence may increase with longer follow-up periods.

DISCLOSURES:

The study received support from the National Cancer Institute of the National Institutes of Health. The Ontario portion of the study was funded by the Institute for Clinical Evaluative Sciences through an annual grant from the Ontario Ministry of Health and Long-Term Care. Additional disclosures are noted in the original article.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.