Answer to Question #4743 Submitted to "Ask the Experts"

Q

I had two head/brain CT scans in January (one week apart) for a sinus infection. I had the second one because my doctor wanted to see the sinuses only but the radiologist went ahead and took my whole head/brain. I called the radiologist at the CT scan department and the radiologist didn't know the amount of radiation that was given. I searched online and found different doses. Can you tell me the amount of radiation dosage for a head/brain CT scan? The CT scan was done at the hospital.

A

It is not unusual to see different dose numbers cited by different investigators for CT or other radiologic exams. The doses will vary considerably, depending on the machine and technique used. In ICRP Publication 62, a representative value of 1.8 mSv (180 mrem) effective dose is given for a head CT. That seems to be a reasonable representation for values I have seen on a number of machines at our institution. Now, this dose is a risk-weighted effective total-body dose (see a frequently asked question answer on the Health Physics Society Web site for more detail). As a head CT does not involve many body organs in the exposed field, the risk weighting factors involved are low. Thus some of the individual tissue in the head area may receive several times this dose value, but the weighted total body average is as shown. For comparison, an average American receives about 3.0 mSv (300 mrem) effective dose from exposure to natural background radiation each year.

Michael G. Stabin, PhD, CHP