Answer to Question #4327 Submitted to "Ask the Experts"

In 1985 my seven-year-old son had a medical work-up to rule out Legg-Perthes disease. At the orthopedic office, he had two pelvic x rays. Both were anterior-posterior (AP) views that included a large area from above his pelvis and his upper femur. I do not know the age of the equipment, but this medical practice had been around for quite some time. Later I found out this equipment did not have rare earth film screens. I am now worried about the dose he received and his future risks. He did not have Legg-Perthes.

We are certainly happy to hear that the results were negative. The amount of exposure received from an x ray of the pelvis is dependent on the size of the patient. With rare earth film screens, an adult receives an exposure of approximately 500 mR to the skin where the x-ray beam enters the body, for example, the entrance skin exposure (ESE), for each x ray. A 12-year-old child receives an ESE of 180 mR and a one-year-old child receives an ESE of 25 mR. My guess would be that a seven-year-old child would be about midway between a one- and 12-year-old child in required ESE. Therefore, I would estimate an ESE of 100 mR per x ray. The use of rare earth film screens typically reduces the exposure required to one-half of that needed with the use of conventional screens. Therefore, I would estimate the exposure for each x ray taken at 200 mR or 400 mR for the two film exams, which is less than that received by an adult for one film using a rare earth screen.

Is this a lot of radiation? Not really. When the radiation exposure your son received from these x rays is compared to the natural background radiation exposure of 300 mR per year, or the total of 6,000 mR since 1985, it is not a lot. The risk from these two x rays is so low that it is inappropriate to even assign a number to it.

Kenneth L. Miller, CHP, CMHP

Editor’s Note: The milliroentgen (mR) is a unit of radiation exposure frequently used in diagnostic radiology for measuring and comparing exposure values.