Answer to Question #4773 Submitted to "Ask the Experts"

Q

I have some health concerns related to medical radiation exposure. I had back surgery when I was a teenager. I had about 20-30 lumbo-sacral spine x rays from age 12 through age 20. All of the x rays were done in China from 1980 to 1988. Recently I searched the Internet and realized that children are more sensitive to the x radiation and have a much increased risk of cancer in later life. So I am very anxious and depressed now.
 
I am 36 years old. Two years ago, I had a lumbo-sacral spine CT scan in Connecticut, which had  nine slices. Five years ago, a doctor in New York City did an injection treatment on my back, which was done under x ray. These x-ray exposures also make me very worried. I think that my cumulative x radiation is a lot.

The supervisor from the radiation department in China told me that they used the same kind of x-ray machine from 1980 through 2000. The data for a lumbo-sacral spinal x ray for an adult is 80 mAS and 65-70 kV. For children, the data is 40 percent p less. He doesn't know the effective dose. They never used a lead apron to cover my abdomen. But he said that they used a lead strip on the machine to reduce the x-ray exposure. I totally don't understand the meaning of the data.

My questions are:

1. Would you please help me figure out how much radiation dose I got?
2. My major concern is I found out that 30 years ago the x-ray dose was 10 times more than now. 
3. What are my increased chances of getting cancer?
   

A

Thank you for your question and especially the additional information you were able to provide about the x rays that were taken in China when you were 12 years old. I am going to use effective dose for all of my estimates and will tell you where I have made some assumptions. I am using two units of effective dose—millisievert (mSv) is used by all countries outside the United States and millirem (mrem) is used in the United States. Both tell you the same thing.

20-30 Lumbar Spine X Rays
Generally, for a lumbar spine series, there are up to five views taken. So, if I assume the 30 x rays totaled six spine series (30 divided by 5) and the effective dose for a lumbar spine series is 1.8 millisieverts (180 mrem), then the total effective dose would be 10.8 mSv or 1,080 mrem.

If I assume they were all flatplate (e.g., you lying flat on your back with the x-ray machine overhead) then the effective dose would be 21 mSv or 2,100 mrem (30 x rays x 0.7 mSv/x ray).

In the extra information you provided, you indicated all these took place in China where, for adults, 60-75 kVp and 80 mAs is used and that the dose for children is approximately 40 percent less. Knowing this, we can multiply the above doses by 60 percent to estimate the doses you might have received as a child. So the 10.8 mSv would now become 6.5 mSv and the 21 mSv would become 12.6 mSv.

Injection Treatment Under X Ray
I make the assumption here that "under x ray" means that fluoroscopy was being used. If that is the case, I am going to assume that the beam on-time was less than one minute and use one minute for my calculations. Roughly, for a minute of fluoroscopy to your lumbar spine, the effective dose is 0.37 mSv or 37 mrem.

If "under x ray" means another flatplate or maybe two, then the effective dose from each would be 0.7 mSv or 70 mrem.

Lumbo-Sacral CT Scan
The effective dose estimate for a lumbo-sacral CT scan is 10 mSv or 1,000 mrem.

Effective Dose Estimate Totals
The effective dose estimate for all these exams would total between 16.87 mSv (6.5 mSv + 0.37 mSv + 10 mSv) and 22.97 mSv (12.6 mSv + 0.37 mSv + 10 mSv).

Cancer Risk
Based on scientific information (BEIR V 1990), we say that the increase in the cancer incidence rate is about 0.05 percent for every 10 mSv of radiation dose based on projections from high doses. That is for adults. It is shown in a new, unpublished report (BEIR VII 2006) that the cancer risk for someone who is 10 years old is about double the risk for a 30-year-old. So, the spine x rays you had when you were 12 years old may have carried a higher risk. However, it is impossible to say that any single person will get a radiation-induced cancer.

But, let's use these numbers to estimate your possible cancer risk. If we use the highest effective dose for the lumbar spine x rays that were taken when you were a child, then we would estimate the risk to be 12.6 mSv x 0.1 percent increase in risk/10 mSv (assuming double the risk). The increased cancer risk from these x rays would then be estimated to be about 0.13 percent.

The estimate of risk from the other x-ray studies you had as an adult would be (.37 mSv + 10 mSv) x 0.05 percent/10 mSv which equals 0.0685 percent.  

Adding it all up, we get about a 0.2 percent increase in cancer risk.

To put that in perspective, the American Cancer Society estimates that about 33 percent of us will get a cancer and about 20 percent of us will die from a cancer. So, with no radiation exposure, you have a 33 percent chance of getting cancer. Adding in the estimated risk from the x rays, your risk today is now 33.2 percent. A small increase.

Although I’ve concluded that the x rays you received involved only a small increased risk of getting cancer, it is important to note that all of this information is estimated. The estimates of medical radiation dose are based on studies that have been done (but not in China), and the estimates of risk are also based on studies of populations exposed to very high doses of radiation. It is important that you do not take this information as definitive but, instead, use it as ballpark figures to determine if there is a need for concern.

Kelly Classic
Certified Medical Health Physicist

References:

Committee on the Biological Effects of Ionizing Radiation (BEIR V). Health effects of exposure to low levels of ionizing radiation. Washington: National Research Council; 1990.

Committee on the Biological Effects of Ionizing Radiation (BEIR VII). Health Effects From Exposure to Low Levels of Ionizing Radiation. Washington: National Research Council; 2006.

Wall BF, Hart D. Revised radiation doses for typical x-ray examinations. The British Journal of Radiology 70:437-439; 1997. (5,000 patient dose measurements from 375 hospitals) The quoted effective radiation doses are all from this source.