BACKGROUND: Computed tomography (CT), a strong diagnostic tool, delivers higher 
radiation doses than most imaging modalities. As CT use has increased rapidly, 
radiation protection is important, particularly among children. We evaluate 
leukemia and brain tumor risk following exposure to low-dose ionizing radiation 
from CT scans in childhood.
METHODS: For a nationwide retrospective cohort of 168 394 children who received 
one or more CT scans in a Dutch hospital between 1979 and 2012 who were younger 
than age 18 years, we obtained cancer incidence, vital status, and confounder 
information by record linkage with external registries. Standardized incidence 
ratios were calculated using cancer incidence rates from the general Dutch 
population. Excess relative risks (ERRs) per 100 mGy organ dose were calculated 
with Poisson regression. All statistical tests were two-sided.
RESULTS: Standardized incidence ratios were elevated for all cancer sites. Mean 
cumulative bone marrow doses were 9.5 mGy at the end of follow-up, and leukemia 
risk (excluding myelodysplastic syndrome) was not associated with cumulative 
bone marrow dose (44 cases). Cumulative brain dose was on average 38.5 mGy and 
was statistically significantly associated with risk for malignant and 
nonmalignant brain tumors combined (ERR/100 mGy: 0.86, 95% confidence interval = 
0.20 to 2.22, P = .002, 84 cases). Excluding tuberous sclerosis complex patients 
did not substantially change the risk.
CONCLUSIONS: We found evidence that CT-related radiation exposure increases 
brain tumor risk. No association was observed for leukemia. Compared with the 
general population, incidence of brain tumors was higher in the cohort of 
children with CT scans, requiring cautious interpretation of the findings.