OBJECTIVE: We aimed to estimate the risks of radiation exposure from a single 
head CT scan to children of different ages.
MATERIALS AND METHODS: We constructed a multistate time-dependent Markov model 
to simulate the course of children exposed to a head CT. The relevant literature 
was reviewed for probabilities, which were used to calculate tumor types, 
latencies after exposure and outcomes in the model. Where multiple 
approximations of the same probability had been reported, meta-analytic 
techniques were employed to compute pooled estimates. The model was then used to 
calculate the effect of the radiation exposure on life expectancy and quality of 
life for children following head CT at different ages.
RESULTS: The tumors likely to be induced by low-level cranial irradiation 
include thyroid carcinoma (47%), meningioma (34%) and glioma (19%). According to 
the model, a single head CT is likely to cause one of these tumors in 0.22% of 
1-year-olds, 30% of whom will consequently die. The exposure will shorten the 
life expectancy of all exposed 1-year-olds by an average of 0.04 years and their 
expected quality of life by 0.02 quality-adjusted life years. The risks of 
radiation exposure diminish for older children.
CONCLUSIONS: The model predicts that the effective radiation dose from a single 
head CT is capable of inducing a thyroid or brain tumor in an infant or child. 
These tumors can severely impact both quality of life and life expectancy. Care 
should be taken before ordering CT scans in children, particularly in infants 
and toddlers.