Answer to Question #4181 Submitted to "Ask the Experts"

Q

I have been reading questions from people concerned with increased cancer risk from CT scans, and understand the potential risk changes from 25% to something slightly higher. Though those statistics appear comforting, they don't address whether radiation will cause cancer sooner than it might appear in the general population. For example, if I am 46 years old, and have a 25% statistical chance of dying from cancer in say 25 years, do I also have a 0.12% chance of dying significantly sooner because of the radiation exposure?

A

It is important to remember that these values are only estimates of risks. The basic risk value of 25% is based on statistical sampling of various regions of the country and of various ethnic groups and ages. As such, it is not appropriate to indicate that this is the risk to any one individual. It is also important to remember that these statistical numbers do and will change based on differences in lifestyle, e.g., less smoking and better diets in some groups, and as better detection and treatment regimes are developed over time. In fact, the odds are you will not die of cancer, e.g., 100% - 25% = 75% of death due to causes other than cancer.

Getting back to your original question, there is clear evidence that a latency period, which is the period between exposure and cancer death, exists for certain types of cancers following high doses of radiation, according to an information sheet developed by contract to the Canadian Environmental Advisory Council. However, I am not really aware if this effect has or can be demonstrated in populations receiving low doses at low-dose rates which are what we encounter in diagnostic radiology exams. My guess is that we all have a predisposition or genetic factor that affects our susceptibility to the development of cancers. In many cases, we die before the induction of the cancer, or before it becomes a significant health factor, e.g., prostate cancer in men over 80 years old. Simply stated, radiation appears to start the development of the cancers at an earlier time, and the higher the dose the earlier the onset.

John P. Jacobus, MS
Certified Health Physicist