Background: Children are more susceptible to radiation-induced damage than adults, but little research has compared the risk of cancer after exposure to radiation during computed tomography (CT) among children at different ages. We aimed to explore the risk of intracranial tumours, leukemia or lymphoma among children, adolescents and young adults (aged < 25 yr) after radiation exposure from CT at or before the age of 18 years.

Methods: We conducted a nested, population-based case-control study using data from Taiwan's publicly funded health care system. We identified participants younger than 25 years with newly diagnosed intracranial tumours, leukemia or lymphoma, from Jan. 1, 2000, to Dec. 31, 2013. We assigned 10 non-cancer controls for each case, matching by sex, date of birth and day of entry to the cohort. We considered CT scans received at or before the age of 18 years and 3 or more years before the index date (the date of cancer diagnosis for cases) as exposure. We used conditional logistic regression models and incidence rate ratios (IRRs) to estimate the relationship between risk of these cancers and CT radiation exposure.

Results: We identified 7807 cases and matched to 78 057 controls. Compared with no exposure, exposure to a single pediatric CT scan did not increase risk of intracranial tumours, leukemia or lymphoma. However, participants exposed to 4 or more CT scans had an elevated incidence (IRR 2.30, 95% confidence interval 1.43-3.71) of one of the cancer outcomes of interest. Receiving 4 or more CT scans at or before 6 years of age was associated with the highest risks of cancer, followed by ages 7-12 years and 13-18 years (p for trend < 0.001).

Interpretation: Exposure to a single CT scan was not associated with increased risks of subsequent intracranial tumours, leukemia or lymphoma among children; however, we observed increased cancer risks among those with 4 or more CT scans, especially among younger children. Although these cancers are uncommon, the findings of this study underscore the importance of prudent use of CT in the pediatric population.