[ RadSafe ] Re 30mCi vs 200 mCi I-131 Therapy

[Perle, Sandy]

Spencer,

You are pretty much correct. That is why I mentioned to Brian that the 26.2 mCi administration I had, and the associated dose measured hourly would be quite different. The comparison of the DIS to the TLD ratio would not change but the dose rate a meter would be significantly higher with the 200 mCi administration. The data I plotted is quite interesting in that it showed that at night, when body totally at rest, the dose rate from the thyroid did not reduce, until there was activity. This of course had nothing to do with elimination from the body since during all hours of activity, the decrease dose rate from the thyroid is observed. Only at night did the dose rate not change. The data was provided to the Nuclear Medicine as well as Endocrinologist MDs and they were fascinated by the data. Consider how often one can measure the dose hourly and be able to plot. The data was also used to calculate how much of the thyroid uptake existed for various times after administration. The only item I would follow-up on is that the 26.2 mCi administration's goal is to basically kill the thyroid cells thus requiring a prescription to off-set the loss of TSH, etc. Blood test are taken routinely now to determine TSH levels and determine when this prescription and at what levels must begin.

Regards,

Sandy

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Sander C. Perle 
President
Mirion Technologies
Dosimetry Services Division 
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-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu [mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of FISHER Spencer -NUCLEAR
Sent: Friday, January 06, 2012 12:33 PM
To: 'radsafe at agni.phys.iit.edu'
Subject: [ RadSafe ] Re 30mCi vs 200 mCi I-131 Therapy

The data for excretion of a 30 mCi or less dose is totally different than that of a 200 mCi dose.  Less than 30 mCi are typically given for hyperthyroidism, in which case the individual still has a functioning thyroid gland.  
Doses of Greater than 70 mCi are typically given for Thyroid Ca, and the patient has had a thyroidectomy, and you are looking to destroy  a little residual tissue and mets.  

And as someone else stated, it is highly variable from individual to individual.

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