Oscillations in Thyroid I-131 levels

[james.g.barnes@att.net]

Folks,

Recently, one of my co-workers had an I-131 thyroid 
treatment done on her pet cat.  Because of concerns that 
she had regarding dose to her family, I provided a survey 
instrument to her for her to check the dose rates on the 
cat (they were not severe, as it turned out).

At my suggestion, she took readings several 
times a day (morning, afternoon, evening).  
Interestingly, she noted that the dose on the thyroid in 
the morning was nearly twice the dose that she would take 
at the end of the day (~ 10 mrem vs. 5-6 mrem).

My interpretation of this is that the thyroid is 
"recharging" itself with thyroid hormones while the cat 
is sleeping, thus increasing the level of I in the 
thyroid.  When the cat is active, these hormones are then 
depleted from the thyroid, causing the lowering in dose.

For you thyroid experts, is this a correct 
interpretation?  Could you provide a more detailed 
explanation?

Thanks,

Jim Barnes, CHP
Radiation Safety Officer
Rocketdyne/Boeing
james.g.barnes@boeing.com 
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