Re: Back-ground Determinati

["Mike Bohan" <mike.bohan@yale.edu>]

        Reply to:   RE>>Back-ground Determination for Thyroid Bioassay

Hi RadSafers:

We use the bioassay subject's shoulder or knee for determining routine thyroid
backgrounds.  This assumes your using a reasonably columnated detector which
adequately shields out most thyroid "shine" and that the subject doesn't have
a metastatic thyroid tumor present in the background areas.  The advantage of
this is that it's quick and the individual's actual background is being used
(similar bone mass in field), so it cancels out K-40 and other isotope
contributions.  

The other proviso is that you should be familiar with your expected background
range, because if you get an unusually high background count by this method
you should suspect that the subject either has significantly high blood
radioiodine levels (Consider immediate KI administration!) or some other
problem (Diagnostic Nuc. Med. Scan lately???, unusual high radon levels???,
radium dial painter???, etc.).

This method is applicable if most of your bioassays are expected to be
negative or close to MDA.  If you get a positive result with significant
uptakes, of course, you may want to modify the procedure and use a derived
background from non-contaminated subjects. 


<><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><
Michael J. Bohan, RSO   |  e-mail: mike.bohan@yale.edu
Yale-New Haven Hospital |    Tele: (203) 785-2950
Radiological Physics    |     FAX: (203) 737-4252
20 York St. - WWW 204   |    As usual, everything I say may be plausibly
New Haven, CT    06504  |    denied at my employer's convenience ...
><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>