Answer to Question #14719 Submitted to "Ask the Experts"

For about a year, I lived with a smoker and was exposed to a lot of secondhand smoke. Towards the end of that year, I had to get a neck computed tomography (CT) scan with and without contrast. I am no longer in that living situation, but I am worried the combined carcinogens increases my risk of getting cancer. Do you have any insight on this? I have read that many people in the Fukushima disaster were smokers, but I cannot find reliable information on the radiation doses they received and their outcomes. Am I worrying unnecessarily?

I want to begin by reassuring you that you don’t need to worry about your CT scan. We know that the risk of developing cancer is higher for people exposed to high radiation doses. However, as stated in the Health Physics Society position paper Radiation Risk in Perspective, the risk isn't statistically different for people exposed to radiation doses below 100 millisievert (mSv) above background compared to those who were only exposed to background radiation.

We also know that exposure to secondhand smoke increases the risk of developing lung cancer and certain other cancers. Unfortunately, the data available regarding the exposure to secondhand smoke is not easily quantifiable and is subject to bias because it is generally self-reported. There were no measurements made of the quantity of smoke in the air. There is a possibility that exposure to radiation and secondhand smoke together increases the risk of cancer more than the smoke alone, but there isn't a lot of data. According to a paper in Ecotoxicology and Environmental Safety, exposures to both smoking and high levels of radon are known to increase the risk of cancer by more than the addition of the risks from each. The good news is that the risk decreases with the time since the exposure.

According to a 2021 article in the Journal of Epidemiology, there has been no data that shows a statistically significant increase of cancer incidence or mortality following the Fukushima disaster compared to prior. The data also show that the incidence trends around Fukushima are similar to those in other parts of Japan that were not affected by the radiation release. Other than the emergency responders at the Fukushima Power Plant, most people were exposed to little radiation from the release and the United Nations Scientific Committee on the Effects of Atomic Radiation has found that "no discernible increased incidence of radiation-related health effects are expected among exposed members of the public and their descendants."

There is much uncertainty in studies that compare cancer incidence in groups exposed to low levels of radiation to those who were not exposed because about 40% of us will be diagnosed with cancer during our lifetimes, whether we are exposed to radiation or not. It isn't possible to tell what caused the cancer in an individual patient, so all we can do is try to determine whether one group has a higher risk than another. There are many risk factors for cancer, including genetics, alcohol use, tobacco use, chemical exposures, diet, hormones, infectious diseases, obesity, and high doses of radiation.

In summary, your risk of cancer is essentially the same as it would have been without the CT scan. If your physician recommends a CT scan in the future, I recommend that you discuss the benefits and the risks of the CT scan, and the risk of not having the scan, then make the decision based on that conversation. I hope this will help you to stop worrying.

Deirdre H. Elder, MS, CHP, CMLSO