Answer to Question #517 Submitted to "Ask the Experts"

Q

When I went for a pelvic x ray recently, a gonad shield was used. I have had many previous x rays (>50) and pelvic CT scans and a gonad shield has never previously been used. I am now worried about the effects that this radiation may have had on my ova. Is genetic damage to any children I may wish to have in the future a possibility?

A

Medical use of radiation should occur only when there is medical justification and the individual benefits from its use. I'm assuming, then, that all of your exams were for some medical benefit. Radiation exposure does carry some risk; with very high doses (higher than one would get from medical diagnostic x rays) risks include the possibility of cancer in the exposed individual and genetic effects in future generations if the ovaries or testes were exposed. I'll answer your question using percentages because I think that might be the clearest way to show the risk in the general population of genetic effects and compare it to the risk of radiation exposure. Current estimates show that for every million live births each year, about 72,900 or 7.29 percent have a genetic disorder. We'll use that 7.29 percent as our baseline for comparison with radiation risk. The ovary dose from a general pelvic x ray varies from about 50 mrad to 100 mrad; the variation is due primarily to the thickness of the pelvis (mrad or mrem are units of radiation dose and are how we quantify that dose; for comparison, the radiation dose we receive annually from natural background radiation is approximately 300 mrem). I'll base my estimate of increased risk of a genetic effect on your having received ten pelvic x rays each year; each time with the ovaries receiving 100 mrad—so, we're estimating 1,000 mrad/y. Remember we have the baseline of 7.29 percent—that there is a natural occurrence of genetic disorders affecting 7.29 percent of live births. When we add the first generation risk of a genetic disorder from 1,000 mrad/y, the risk increases from 7.29 percent to 7.305 percent. These numbers are extrapolated from higher doses but represent our best current estimates. So, there is an increased probability of a genetic disorder but it is very small. The medical benefit of the x-ray exams far outweighs this risk. As for the gonadal shield—it is not often that a shield can be used during a pelvic or abdominal film because there is a good chance that it might cover part or all of what needs to be seen. A gonadal shield should be used if possible, during abdominal or pelvic x rays. When you have a lower abdominal x-ray exam performed, you can ask to have a gonadal shield. You might get the response that it will interfere with the exam and can't be used, but occasionally there might be a circumstance when they can use it. If you have access to a library which has the following references you might find them useful. References:

• United Nations Scientific Committee on the Effects of Atomic Radiation. Sources and effects of ionizing radiation. 1993 Report to the General Assembly with scientific annexes. United Nations, New York; 1993.
   
• National Research Council. Health effects of exposure to low levels of ionizing radiation. Committee on the Biological Effects of Ionizing Radiations. National Academy of Sciences, Washington DC; 1990.
   
• Hall, E.J. Radiobiology for the radiologist, third edition. J.B. Lippincott Company, Philadelphia; 1988.

Kelly Classic Certified Medical Health Physicist