Exposure to diagnostic low-dose ionizing radiation and CT scans is associated with increased cancer incidence in children, according to a new study in more than 12 million South Korean youth.

“The associations we found of diagnostic low-dose ionizing radiation with increased incidence of cancer in youths suggest that there is incentive to limit radiation doses to as low as reasonably achievable and to only scan when justified,” Dr. Jae-Young Hong of Korea University in Seoul and colleagues write in JAMA Network Open.

“Medical professionals should weigh the benefits of diagnostic low-dose ionizing radiation with the associated risks to justify each decision,” they add.

The investigators analyzed South Korean National Health Insurance System claims data on a cohort of more than 12 million children up to age 19 at enrollment in 2006 who were followed through 2015.

Exposure to diagnostic low-dose ionizing radiation occurred in 10.6%, including 178,518 who had more than one scan.

There were 21,912 cancers diagnosed during follow-up, including 1,444 (0.1%) in individuals exposed to diagnostic low-dose ionizing radiation at least two years before they were diagnosed.

After adjusting for age and sex, diagnostic ionizing low-dose radiation exposure was associated with a significantly increased incidence of cancer (incidence rate ratio, 1.64; P<0.001). Exposure to CT scans was also associated with increased cancer risk (IRR, 1.54; P<0.001).

Radiation exposure was also linked to significantly increased risk for both lymphoid and hematopoietic cancers (IRR, 1.53), particularly other myeloid leukemias (IRR, 2.14) and myelodysplasia (IRR, 2.48); and solid cancers (IRR, 1.70), especially breast (IRR, 2.32) and thyroid (IRR 2.19).

“Our findings raise concerns regarding the use and subsequent risks of diagnostic low-dose ionizing radiation exposure in youths,” Dr. Hong and colleagues write.

“Risk analysis in the United States suggests that, for children, the lifetime excess risk of any incident cancer for a head CT scan is approximately 1 cancer per 1000 to 2000 scans,” they add.

“Therefore, the absolute excess lifetime cancer risk is small compared with the lifetime risk of developing cancer in the general population, which is approximately 1 in 3. Provided that imaging is clinically justified, it might be appropriate in a younger patient who needs correct diagnosis.”