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

Category: Medical and Dental Patient Issues — Diagnostic X Ray and CT

The following question was answered by an expert in the appropriate field:


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 4 mGy* (air kerma) 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 0.22 mGy (air kerma). 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 0.88 mGy (air kerma) 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 1.75 mGy (air kerma) or 3.5 mGy (air kerma) 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 2.6 mGy (air kerma) per year, or the total of 52.6 mGy (air kerma) 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 millirogray (mGy) is a unit of radiation dose or kerma in air and is used in diagnostic radiology for measuring and comparing exposure values.

*Note: To convert to traditional radiation exposure units: 1 mGy (air kerma)= 114 mR.

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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