Answer to Question #10271 Submitted to "Ask the Experts"

I would like to ask how to appropriately handle food and drinks in an office setting that performs nuclear cardiology studies. No radioactive aerosols or gases are used. If there is a delineation mark in a scanning room that divides the work area from the radioactive materials storage area, is it appropriate and allowable to eat and drink in this room? I have always worked in the hospital where rooms are clearly separated and defined and would like clarification if the delineation is permissible or not.

The question as I understand it is whether it is appropriate to allow eating and drinking in a designated/delineated area of a nuclear cardiology scan room. Let's start with some assumptions and see what happens:

Assume: 

1. Each patient receives 1,480 MBq (e.g., the patient is on a 1,110 MBq stress/370 MBq rest protocol).
2. 60 patients per week.
3. 50 weeks per year.
4. All dosages are received in the morning, so total activity received is two times the administered activity.

The total activity received in a year is 2 x (1,480 MBq/pt x 50 pt/week x 50 pt/y) = 7,400,000 MBq.

According to Allen Brodsky, one should expect less than 10^-6 for "the fractional amount of radioactivity placed into process in routine operations that will enter the body of any worker, averaged over an extended period (e.g., one year)" (Brodsky 1980). This leads to an uptake of less than 8.88 MBq. 

The annual limit on intake is 2,960 MBq (10 CFR 20 Appendix B). Since this amount corresponds to an internal dose of 50 mSv, 8.88 MBq would correspond to a dose of 0.15 mSv per year from uptakes. Expending considerable time and effort for a 0.15 mSv per year reduction for a few people is not consistent with the philosophy of keeping doses as low as reasonably achievable, as it violates the "reasonable" aspect. In other words, there is little risk to employees in this situation.

Another way to look at it is scenario driven:

When contamination occurs, there is some means of transferring it from its origin to other areas. In other words, contamination is spread by contaminated gloves, shoes, hands, articles, or equipment, etc. I have never seen a doorway that removes contamination as one passes through it. Delineation, therefore, serves the same purpose. There should be three rules regarding leaving the scanning room and entering the eating area (whether this involves leaving the room or crossing a delineation):

1. Remove gloves and laboratory coat before entering area.
2. Wash hands upon entering area.
3. Include the area on routine surveys.

But your regulator may see things differently. To my knowledge, neither the Nuclear Regulatory Commission nor any state radiation control agency has regulations that specifically prohibit eating and drinking where radioactive materials are used. However, there could be a statement prohibiting eating in areas where unsealed radioactive materials are used in the license application submitted to the regulatory agency to which you are obligated. Check your license, license application, and policies and make sure that there is no conflict with what you are committing to do in your workplace.

There are other considerations that may make this a poor practice, such as control of blood-borne pathogens. 

Kent Lambert, CHP

Reference
Brodsky A. Resuspension factors and probabilities of intake of material in process (or "is 10^-6 a magic number in health physics?"). Health Phys 39(6); 1980.