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07 October 2008

Answer to Question #1836 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:

I recently underwent two x rays of a finger—one of 40cGy and the other of 50 cGy. I work for a nuclear power company where the staff is subject to very stringent limits of radiation exposure. For my own amusement, I attempted to convert my x-ray exposure to a total-body dose and came up with a figure of 50mSv or five times the annual limit allowable for staff in my company. Did I do my sums right?

To begin with, you have your units wrong. 40 to 50 cGy (40 to 50 rad) is an absurd dose for a finger x ray. An x ray of a finger requires little exposure. 40 to 50 µGy (microgray) (4 to 5 mrad) would be a typical finger dose. Above and beyond that, I am not sure how to (or even if it is appropriate to) convert such a dose to a whole-body equivalent dose. But, let's say for the sake of argument that we use your conversion assumption that the occupational extremity dose limit is 10 times higher than the whole-body dose limit; therefore, 10% of an extremity dose is the whole-body dose equivalent. That would yield a 4 to 5 µGy (0.4 to 0.5 mrad or 0.004 to 0.005 mSv) whole-body dose equivalent. Hope this helps. Kenneth L. Miller, CHP, CMHP Penn State Hershey Medical Center

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