Answer to Question #12711 Submitted to "Ask the Experts"

We will be using iodine capsule (¹³¹I ) with a maximum activity of 7.4 gigabecquerels (GBq) in our nuclear medicine hot lab. We need to order a new iodine fume hood to be used within the facility. Can you please provide a recommendation related to iodine hood specifications in terms of filter type, air flow, and shielding?

A search on the internet reveals a number of charcoal-filtered fume hood options, however, you may want to consider if you really need a charcoal-filtered hood. After an extensive search of the literature, the last scientific publication on the volatility of radioiodine from capsules that I could find was published in 2000 (Bright et al. 2000). From that reference, the highest activity released from one of the ¹³¹I capsules was listed as about 0.1%.

I contacted a number of radiation safety officers (RSOs) and none of them require nor see the need for a charcoal-filtered fume hood for storing and handling ¹³¹I capsules. These opinions were based upon a number of years of air monitoring, thyroid bioassays of nuclear medicine staff, and the fact that the preparation of the ¹³¹I capsules by the nuclear pharmacies are performed in such a way to minimize the potential for volatile radioiodine. In case of unusual circumstances, one RSO recommended storing and opening the capsule containers in a standard chemical fume hood and I would concur with that recommendation.

A number of years ago, I measured the volatile activity from ¹³¹I patient doses provided as an oral solution. Frankly, I can't remember the results of that except to say that we did find measurable amounts of volatile ¹³¹I in the airspace above the liquid. That merely serves to illustrate that oral solutions may be more likely to include a volatile component than capsules.

Thus, I would recommend the following actions with respect to the need for a charcoal-filtered hood:

1. Contact your regulator to see if they require a charcoal-filtered fume hood and, if so, their basis for such a requirement.
2. Store and, as an added precaution should some unusual event (e.g., ruptured capsule) result in a small release of volatile activity, initially open the capsule container in a fume hood that is vented to the outside (as opposed to recirculated back into the room air). If necessary, you or your RSO could perform some calculations based upon the potential amount released as cited in the above reference and the airflow of the fume hood to show that release limits to the environment would not be exceeded.
3. If you (or your regulator) still feels a charcoal-filtered hood is required, simply search the internet and/or suppliers of nuclear medicine equipment and you should find something suitable.

Mack L. Richard, MS, CHP

Reference

Bright JM, Rees TT, Baca LE, Green RL. Volatility of radiopharmacy-prepared sodium iodide-131 capsules. J Nucl Med Technol 28:52–55; 2000.