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?
Answer: (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)