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:

Q

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.

A

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.

Answer posted on 8 March 2005. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.