Answer to Question #408 Submitted to "Ask the Experts"

Q

With regard to ALARA Investigational Dose Levels for External Dose Monitoring, as described in NUREG-SR1556 V9 and elsewhere, the levels for whole body and lens are the same (125/375 mrem/qtr Levels I/II) even though the MPEDE for the lens is three times greater than for the whole body. Is that a misprint? Also, what does "skin of whole body" mean for a medical worker wearing an apron? Is it standard practice to use the "shallow" badge reading (badge at collar outside apron) for "skin of whole body" even though the worker wears an apron?

A

No, there is no misprint in the table. Note that there is no fixed relationship between the recommended action levels and the corresponding annual dose limits; in other words, the Level I and Level II action levels do not represent fixed fractions of the dose limits for the corresponding organs or tissues to which they apply. The other point to note is that it would not be very useful to specify separate action levels for the eyes because there are very few situations in which the lens of the eye alone will be exposed, without concurrent exposure of other parts of the body, such as the head or the skin. Therefore, because any exposure to the head (which is part of the whole body) above 125 mrem per quarter (Level I) will be investigated, so therefore will the attendant exposure to the eyes. This is a much simpler approach than having a separate action level for the eye, one that would rarely, if ever, be used by most licensees. Of course, if a very unusual situation arises in which only the lens is exposed, then there is nothing in the regulations or guidance that prevents the licensee from establishing action levels for this special case that may differ from those recommended in the table. Skin of the whole body is used in the table only to help distinguish it from skin of the extremities. In specifying dose limits, 10 CFR Part 20 does not make such a distinction, but only refers to "the skin" and "the extremities." Part 20 also goes on to require that "the assigned deep-dose equivalent and shallow-dose equivalent must be for the part of the body receiving the highest exposure."



For the case of the medical worker wearing an apron, the dose to the skin is the highest dose to any one square cm of skin (part of the definition of shallow-dose equivalent), anywhere on the body, other than the extremities. This is typically the dose to the skin of the head or neck area if the rest of the body is shielded by an apron and other intervening equipment. Hence the use of the collar badge to measure the shallow, or skin, dose. The fact that much of the worker's body is shielded from the radiation does not affect this requirement.



Sami Sherbini