Health Physics Questions and Answers - Question 175
Question 175: A health care worker serves in a dual nuclear medicine and radiology position. The worker wears a dosimeter on the waist and a dosimeter at the collar. During fluoroscopy procedures, which is the primary source of exposure, the worker wears a lead apron that covers the waist dosimeter, but not the collar dosimeter. Over the course of a year, the worker receives a dose of 5.2 rem as measured by the collar dosimeter and 1.7 rem as measured by the waist dosimeter.
(a) Has the individual been overexposed?
(b) Can licensees take credit for shielding while monitoring the external dose component of the TEDE?
(a) Yes, the individual has received a dose in excess of 10 CFR 20.1201 limits. The head and neck constitute part of the "whole body", and in this case, received the highest exposure. The collar dosimeter measured a dose of 5.2 rem over the course of a year. If the head and neck were not shielded, and if the collar dosimeter was a measurement of the dose to the head and neck, then the dose exceeded the limit of 5 rem TEDE.
(b) The licensee can only "take credit" for shielding if it can be shown that the dose monitored behind the shielding is an accurate measurement of the maximum deep dose equivalent to the individual. Many shields used for radiation protection do not cover all of the upper legs, upper arms, and/or neck, and few if any shields protect the head from external radiation. Therefore, few shields would satisfy the conditions for credit. However, licensees should use shielding as necessary to minimize the area of exposure and keep doses ALARA.
(Reference: 10 CFR 20.1201)