More About Radiation

Some more detailed information (that some people may want to skip):

What’s the Math?

A medical CT examination with an effective dose of 10 millisieverts (abbreviated mSv; 1 mSv = 1 mGy in the case of x rays.) may be associated with an increase in the possibility of fatal cancer of approximately 1 chance in 2000.


A dental CBCT scan exposes patients to a much, much lower effective dose than most medical CT scans. In our office we use a J. Morita F40 small field of view CBCT scanner. Compare 10 millisieverts for a medical CT to 0.015 to 0.032 millisieverts for our dental CBCT (15-32 microsieverts depending on the region of the jaws). The dose is hundreds of times lower.

10mSv / 0.015 mSv = 667 times LESS radiation

10mSv / 0.032 mSv = 312.5 times LESS radiation

So, if a medical CT scan with an effective dose of 10 mSv increases the risk of a fatal cancer by 1 chance in 2000, then, for our dental CBCT the risk is in this range: between 1 chance in 625,000 (2000 x 312.5) and 1 chance in 1,334,000 (2000 x 667). Take the average those 2 and you get about 1 chance in a million.

In other words, for any one person the additional 1 in a million risk of radiation-induced cancer from a dental CBCT or X-ray film is negligible compared to the natural 1 in 4 risk of cancer.

What does 1 in a million really mean?

Most people have trouble putting probabilities like this into perspective. Here are some helpful comparisons. The following list are things that have a one in a million chance of killing you (sometimes called micromorts).

  • Drinking 0.5 litres of wine (cirrhosis of the liver)
  • Smoking 1.4 cigarettes (cancer, heart disease)
  • Walking 17 miles
  • Riding a bicycle 20 miles
  • Travelling 250 miles in a car
  • Travelling 6000 miles by jet (cancer due to increased background radiation)
  • Living in Winnipeg for 1.78 days (background radiation – see below)
  • Living 2 months with a smoker (cancer, heart disease)
  • Drinking Miami water for 1 year (cancer from chloroform)
  • Eating 100 charcoal-broiled steaks (cancer from benzopyrene)
  • Eating 40 tablespoons of peanut butter (liver cancer from aflatoxin B)

Let’s get specific for Winnipeg:

Living in Winnipeg we are all exposed to 4.1 mSv of background radiation per year. So, it takes 2.439 years of living in Winnipeg to receive 10 mSv which, as mentioned above, adds a 1 in 2000 chance of developing a fatal cancer. So, what does it take to have a one in a million chance? 1.78 days! (2.439/500=0.004874 years X 365 = 1.78 days) You have a one in a million chance of developing a fatal cancer just by living in Winnipeg for less than 2 days. This is the amount of additional radiation you are exposed to with a dental CBCT scan.

American Association of Physicists in Medicine: The calculations above may actually OVERSTATE the cancer risk from medical and dental imaging. In their 2018 position statement, the American Association of Physicists in Medicine state: “…epidemiological evidence supporting increased cancer incidence or mortality from radiation doses below 100 mSv is inconclusive…Given the lack of scientific consensus about potential risks from low doses of radiation, predictions of hypothetical cancer incidence and mortality from the use of diagnostic imaging are highly speculative”. And remember, that 100 millisieverts is hundreds of times more than our dental CBCT (0.015 to 0.032 millisieverts).

Selected References:

Subjecting Radiologic Imaging to the Linear No-Threshold Hypothesis: A Non Sequitur of Non-Trivial Proportion Jeffry A. Siegel, Charles W. Pennington, and Bill Sacks; J Nucl Med 2017; 58:1–6