Answer to Question #14907 Submitted to "Ask the Experts"

Due to health issues, I have had seven computed tomography (CT) scans over the last six months. My total radiation dose is now at 53 mSv. I've been a sobbing wreck. Does the timing between the CT scans make a difference. Does receiving a radiation dose in six months that is over the 50 mSv annual limit make me more at risk? The technologist that did my last CT scan said being smaller helped and I won't absorb as much radiation. The technologist also said lying flat helps too. Does this mean I didn't "absorb" all of the 53 mSv?

I am very sorry to hear about your recent health issues necessitating multiple CT scans. This must be a very scary time for you.   

Let's start our discussion with the 50 mSv annual limit you are considering. The value of 50 mSv is the annual limit for radiation workers. It is the amount of radiation that individuals can receive year after year with the expectation of minimal or even no health risk as a result of their lifelong careers as radiation workers. There are no annual radiation exposure limits for patient exposures. Radiation should be used as indicated by the presenting medical condition and not an imposed limit on patient exposure. Receiving 53 mSv over six months won't change your risk which is still low or even non-existent. The Radiation Answers website, developed by the Health Physics Society, says a dose of 50–100 mSv received in a short period or over a long period is safe—we don't expect observable health effects. At this level, an effect is either nonexistent or too small to observe.”

The dose information provided by the CT scanners is all based on dose to a phantom, not to you personally. A phantom is an acrylic model of a human body in which dose may be measured to mimic potential dose in a human. Your personal dose will vary based on your size in comparison to the phantom. Based on the CT technician's comment, you may be smaller than a phantom and it would be reasonable to expect that your exposure may be lower that reported by the CT equipment. The dose numbers are used by medical centers to verify correct settings and for comparing to other centers to make sure they are not using too much or too little radiation for CT studies.

Please remember that if a physician is ordering diagnostic imaging, then there is clinical health information that the physician is seeking so as to provide the best possible medical care for you. I know it can be scary having study after study performed. I too have had numerous CT studies over the past 14 years that started with a flurry of CTs in one month. Please understand that there could be a definite health risk associated with not completing an ordered exam that could have immediate implications to your health.

I hope this helps add perspective and understanding to what can be a very complex discussion. I understand that it feels like a lot of radiation in a short time frame, but I hope you can now feel reassured that you do not need to fear any health effects from the exposures you have received.

Kendall Berry, MSPH