Re: Mecial Question

[carol marcus <csmarcus@ucla.edu>]

At 01:25 PM 2/29/00 -0600, you wrote:
>We have a worker about to undergo a thyroid ablation.  He is scheduled for
>an "uptake test."
>
>Can someone enlighten me on what this is?  Particularly, if it is a nuclear
>medicine procedure with a smaller administration of I-131?
>
>Matt Williamson
>Indian Point Unit 3
>Williamson.m@nypa.gov <mailto:Williamson.m@nypa.gov> 	
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Dear Matt:

A nuclear medicine thyroid "uptake test" preceding thyroid ablation for
hyperthyroidism is almost always done with I-131 or I-123.  A "metastatic
survey" before the ablation of thyroid remnants in the case of thyroid
cancer is usually done with I-131, but some physicians use I-123.

In the hyperthyroidism case, a small dose of I-131 (about 10 microCi) is
used; if there is to be imaging as well in order to estimate gland size, it
is done with about 5 mCi Na pertechnetate-Tc-99m.  With Na I-123, 100-400
microCi is used, and imaging as well as uptake may be done with this
radiopharmaceutical.

In the case of thyroid cancer, doses of 500 microCi to about 10 mCi of Na
I-131 are used.  If Na I-123 is used, about 10 mCi of that agent is typical.

The halflife of I-123 is 13 hours, and these days is available virtually
contamination-free.  I-124 is there in extremely small quantities, and is
probably not measurable with external detectors.  

Hope this helps.

Ciao, Carol

Carol S. Marcus, Ph.D., M.D.
<csmarcus@ucla.edu>

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