Answer to Question #12755 Submitted to "Ask the Experts"
Category: Medical and Dental Patient Issues
The following question was answered by an expert in the appropriate field:
I am a 53-year-old female. Over the past 11 years or so I have had two barium swallows and two mammograms. After my last barium swallow, I was informed that my radiation dose was approximately 0.6 mSv and that I had a 1 in 33,000 risk of cancer and 1 in 49,000 risk of cancer from my mammograms. I am presuming these calculations are from the linear no-threshold (LNT) model and that the risk is theoretical. I have read a number of articles on the internet about cancer risks associated with medical imaging. I was reassured by your website and the HPS statement in relation to doses below 100 mSv and cancer risk and other information available regarding radiation. My internet review left me with two questions.
- Why is the LNT model still used if the risk of cancer associated with medical imaging is "too small to see?"
- Has radiation been studied significantly to support the theory of an increase in cancer at levels only above 100 mSv? I have been told that the amount of radiation I received was equivalent to months of naturally occurring background radiation. Is it as safe to receive months of radiation all at once?
I am really anxious since having my recent tests and would be grateful for a response.
The answers to your questions follow:
- As the radiation protection sciences have evolved over time, various studies have been undertaken to determine if the LNT model was accurate. During that time, the LNT model has continually been used as a very conservative approach for radiation protection decisions.
Here's a nonradiological example that may help: the data is clear that the more miles you drive your car, the more likely it is that you may be in an accident. But does this relationship apply to when you are just moving your car 3 m in front your house? Now this doesn't mean you shouldn't still drive safely at all times, but the risk of driving 3 m is likely quite different that driving millions of km in a year. So, the LNT model is a good model to use for radiation protection decisions—in other words, to decide what steps can be taken to reduce doses to as low as reasonably achievable, but we should also keep in mind the important clinical benefits of the procedures you describe.
- No one can definitively say that there is absolutely no risk associated with radiation doses below 100 mSv, but the risk (if any) is so low that it pales in comparison to other well-known everyday health risks. Your comment about the doses being equivalent to the annual dose received in the United States is accurate. The National Council for Radiation Protection and Measurements estimated the average annual dose to a member of the public from ubiquitous background radiation to be 3.1 mSv.
I would strongly recommend you access the Imagine Gently website that speaks to exactly the questions you are asking and provides some very reasonable steps to work with your health care provider to assess the necessity, risks, and benefits of the exposures you're describing.
Robert Emery, DrPH, CHP, CIH, CBSP, CSP, CHMM, CPP, ARM