Answer to Question #11859 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
I am concerned about my baby girl's health. She had a computed tomography (CT) scan of her head and face (both at the same time) when she was seven weeks old to rule out craniosynostosis. I wasn't really aware at the time about the amount of radiation that CT scans use and the possible cancer risk increase for children. The CT scan was taken at a children's hospital, and the dose she received was 1.727 millisieverts (mSv). Looking online I found that the average dose is 1.5 mSv for a head CT scan on children 0–5 years old.
My first concern is: Why, if my baby was so young at the time, would they allow her to receive more than the average dose? I am aware that the dose received would be correlated to the weight and size of the patient.
My second concern is: How much is risk increased for babies that young after a CT scan delivering the radiation dose my baby received? I am a very concerned mother who has been worrying for months by now. An honest response would be really appreciated.
You did the right thing by your child and did not put her at any real risk. The risks of health effects from radiation doses received during diagnostic imaging procedures, including head CT scans, are either too small to be observed or are nonexistent. For this reason, the Health Physics Society recommends against quantitative estimates of health risks for radiation doses below 100 mSv. The benefits from properly performed, clinically indicated, diagnostic imaging procedures, including CT scans, far outweigh any hypothetical cancer risk.
You give the average dose from a head CT scan to a child between 0 years and 5 years of age as 1.5 mSv. Because a seven-week-old child is smaller than a five-year-old child, the newborn's internal organs are closer to the primary radiation beam and therefore those organs receive more radiation that scatters (bounces) off the head.
This means that given the same dose to the head, the dose to the rest of the body will be greater for a five-month-old child than it would for a five-year-old child. CT doses also depend on where the imaging starts and stops. This can vary depending on the child’s head size and the needs of the exam.
I should also point out that doses in mSv are calculated based on models, i.e., standard sizes and distances—they cannot be measured. Although you cited a dose of 1.727 mSv, the effective dose your child received cannot be known to the accuracy implied by the number of decimal places indicated.
Kent Lambert, CHP, FHPS