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.  

  1. Why is the LNT model still used if the risk of cancer associated with medical imaging is "too small to see?"
  2. 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:

  1. 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.
  2. 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.


Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
Answer posted on 5 February 2019. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.