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08 February 2012

Answer to Question #4151 Submitted to "Ask the Experts"

Category: Medical and Dental Equipment/Shielding — Shielding

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

I am a registered CT (computerized tomography) technologist and have a question regarding shielding of pediatric patients. I have been told by someone who went through a registered program that pediatric patients should not be shielded due to the fact that the radiation may be "trapped" between the two lead shields. I have always been taught to shield anyone younger than childbearing age. Could you shed some light on the safest way to scan a child and how to shield one properly?

As you will recall, x rays travel at the speed of light. Along their path, they interact and scatter, interact and get totally absorbed, or do not interact at all and continue traveling in a straight line. All of this happens at the speed of light. X rays do not get trapped between two sheets of lead or two sheets of any other material. The majority of the exposure to tissue out of the tissue volume being analyzed during the CT exam comes from radiation scattered within the scanned volume. There is no way to shield for this scatter radiation that occurs within the body. A better method of protecting pediatric patients is by making certain that proper pediatric techniques are used in performing the study. A good reference is Boone JM, Geraghty EM, Seibert JA, Wooten-Gorges SL. Dose reduction in pediatric CT: A rational approach. Radiology 2003; 228:352-360.

Kenneth L. Miller, CHP, CMHP

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