Re: I-131 THERAPY DOSES AT NUC MED FACILITIES

[avest@magnus.acs.ohio-state.edu (Albert Lee Vest)]

>
>Dear Reader:
>
>I understand that a fraction of iodine-131 therapy doses volatilizes and
>escapes the open vial.  

Please see the journal Health Physics, Vol. 36 (January 1979), pp. 68-69.  
It's a research note from some Ohio State people - Richard D. Myser and 
Robert W. Pollack - touching on this very subject.  I quote:  "... upon 
opening a container of NaI solution, a cloud of radioiodine is released, and 
then a steady-state vaporization rate is quickly reached.  With a 30-mCi NaI 
solution, this steady-state rate was 0.005 microCi/min."  Techniques for 
keeping air concentration down during transport and administration are also 
discussed.  

>I am wondering what methods do other Nuclear
>Medicine facilities use to  account for this fraction and show effluent
>concentration is within DAC. We in-line sample the exhausted air using 
>charcoal filter.  A 12,000 CFM
>outside air is introduced to the air exhaust from our Nuclear Medicine hood.

That's a lot of air!  If you can show the volatilization does not exceed 
14.6 microCi/minute, then you've shown the emission concentration is below 
DAC.  Too bad the EPA doesn't use DAC as a criterion . . .

>If you sample the air using activated charcoal, have you
>detected any I-131?  I thank you for your forthcoming response.

We've taken samples from the exhaust from one of the Nuclear Pharmacy hoods, 
because they iodinate a lot with I-125.  Usually monoclonal antibodies for 
use in radioisotope-guided surgery (RIGS).  In a few samples, I've noticed 
an I-131 peak, but I-125 always predominates.  

NP added a charcoal filter to the hood last year (not in-line, but right at 
the air inlet, on the ceiling of the hood chamber).  It hasn't seemed to 
reduce the emission rate much.  How effective is yours?
Albert Lee Vest    avest@magnus.acs.ohio-state.edu
health physicist        Office of Radiation Safety
(614)292-0122            The Ohio State University
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