calibration for thyroid uptake measurement

[Malek Chatila <mc02@aub.edu.lb>]

Dear Radsafers,

I am in the process of setting up a bioassay program to measure thyroid
uptake for I-131.  I have a complete gamma spectroscopy system (Canberra
INSPECTOR) with 3" X 3" NaI detector and a thyroid phantom (ANSI/IAEA).
In order to calibrate (energy and efficiency) the system, I was thinking of
placing 0.2 uCi of Eu-152 in the thyroid phantom, then running the analysis
routine that will calibrate the system for both energy and efficiency over
the entire energy spectrum.  I figured that Eu-152 would give at least 4
distinct peaks, which will allow me to make full energy and efficiency
calibration.  Once I have the system calibrated, then I can make thyroid
uptake measurements by taking reading then running an analysis routine to
identify and measure the present activity.  
I have two questions that I was hoping you might assist me with.  First, do
you think the above mentioned procedure will be adequate? Please comment.
Second, what will the physical characteristic of the Eu-152 source should
be?  I guess what I am trying to say is that I know that when you want to
make efficiency calibration, you need to have similar geometry between the
calibration standard (Eu-152) and what ever you are trying to measure.  So
in order to obtain this similarity, do I need to have the Eu-152 dissolved
in some liquid and place it in one of the thyroid phantom polyethylene
vials? Or can I have it in a capsule form and use the capsule holder that
comes with the phantom?
As always, thanks in advance for your assistance.

Sincerely,

Malek Chatila
American University of Beirut
Email: mc02@aub.edu.lb
Fax: 961-1-749-198


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