Answer to Question #2866 Submitted to "Ask the Experts"

Q

I am a 33-year-old woman. About three months ago I suffered from acute back pain. I went to see a physiotherapist and my back improved but was not back to normal in two weeks time. I decided to get the opinion of my general practitioner (GP) and she suspected a prolapsed disk and said that I should get a CT scan to confirm the diagnosis. I asked her whether I can get an MRI and her reply was that a CT scan is better. So I went to have the CT scan which confirmed the diagnosis. I felt a bit nauseous after the scan was taken. I asked my GP upon return how much radiation a CT scan was compared to an ordinary x ray and she replied that "it is the same but that they make slices." When I asked her about the effects on my ovaries she answered that she wouldn't know. I found out the amount of radiation is 10mSv by calling the radiologist and from information on the Internet. I also found information on a Web site on prolapsed disks and they suggested that in most cases x rays or CT scans are not necessary for this problem. My back is fine now. I changed GPs and my new GP said that he would not have ordered the CT scan for my case. I am angry that I have not been given prior proper information and that there was absolutely no benefit for me from this procedure. I am very afraid that I will develop bone-marrow cancer from the scan and that I won't be able to have children. During the last three weeks I have suffered from abdominal pain, but an ultrasound scan did not detect any cysts. My menstrual cycles have been shorter over the last two months. I have been worrying for the last four weeks about possible radiation effects and searched the Internet for information. I feel sad and depressed and unable to concentrate on my work. I am afraid that I am more sensitive to the effects of radiation than other people. I miss expert advice. Could you help me please?

A

I am confused by your comments. You say that your first GP suspected a prolapsed disk and recommended a CT scan to verify this suspicion. The CT scan did, indeed, verify the diagnosis. Therefore, it would seem that the CT scan was a proper procedure for your condition and symptoms. At any rate, I am not about to second-guess any of the physicians involved. Let me address your concerns about the radiation involved.

The radiation dose from natural background radiation (radiation that we all are continuously exposed to from cosmic rays, radioactive materials present in the earth and building materials, and radioactive materials normally present within our own bodies) is approximately 3 mSv per year. Therefore, in every three-year period you receive the equivalent of a CT scan from natural background radiation. At age 33, you have received the equivalent of 10 CT scans from background radiation. The symptoms that you described, that is, nausea, abdominal pain, and shortened menstrual cycles, are not symptoms associated with such low doses of radiation. In fact, there are no clinically detectable effects from such low doses of radiation.¹ Will you develop bone marrow cancer from this radiation dose? Not likely. Will the radiation dose affect your ability to have children? No. Is there anything that we can say for certain about the level of radiation that you received from the CT scan? Yes. One can say, "It is impossible to predict what, if any, cancer risk might exist from this low dose of radiation. If there is a risk, it is extremely low."

Epidemiological studies of various groups, for example the atom bomb survivors in Japan, have shown that there is an increased risk of developing cancer when the radiation dose is high. There have not been any studies that have demonstrated a proportionate risk for low doses.

Incidentally, there are places around the world where the natural background radiation dose is as high as 150 mSv per year and the populations living in such areas show no increased incidence of cancer. I hope this helps to answer your questions.

Kenneth L. Miller, CHP, CMHP

¹Editor's note: The Health Physics Society has also released a position statement that says in part "Below 10 rem (100 mSv) . . . risks of health effects are either too small to be observed or are non-existent."