Answer to Question #10599 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
Scan parameters were:
Total mAs: 4,159
Total DLP (dose length product): 2,156
I read that to get the total radiation dose in mSv, I need the conversion rate which I found on the Internet. For the head of an adult person it is 0.0021. So, 2,156 × 0.0021 = 4.5 mSv. How do I know they used a conversion rate of 0.0021 and did not use 0.0053 for example? If they used a conversion rate of 0.0053 (the conversion rate for a neck scan or for a baby scan), the total radiation is 11 mSv. Is there any proof that they used a conversion rate of 0.0021?
Please help me. I’m 26 years old. Did that unnecessary scan I got two years ago destroy my life?
A nationwide survey of CT examinations conducted by the Council of Radiation Program Control Directors indicates the median effective dose for an adult head CT scan is 2.5 mSv. The effective dose estimate for each scan you received is 2.26 mSv (4.5 mSv for both scans). In other words, the estimated effective dose you received is about the same as the typical doses seen nationwide.
The American Association of Physicists in Medicine states that the “risks of medical imaging at effective doses below 50 mSv for single procedures or 100 mSv for multiple procedures over short time periods are too low to be detectable and may be nonexistent.” The effective dose estimate from your CT scans is well below these levels and involves minimal, if any risk.
Karen Brown, MHP, CHP, DABR
Steve King, MS, CHP, DABMP
Editors’ Note: Even if CT scans or other diagnostic images do not reveal anything wrong, they should not automatically be considered unnecessary. These exams eliminate possible causes of the medical condition and this is important information to know.