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Re: Tl-201



At 04:25 PM 8/1/02 -0400, Kurt R. Geber wrote:
Does anybody have info on the biological half-live of Tl-201 used in stress tests.  Does the inability to pass a portal monitor for 30 days seem excessive?

Kurt R. Geber
NASA Project Radiation Safety Officer
Dear Kurt:

According to ICRP #63, p. 371, 80% of Tl-201 is excreted by the GI tract, and 20% by the kidneys.  The whole body retention curve can be represented by a two-exponential function with half-times equal to 7 days for 63% and 28 days for 37% of the injected activity.

Tl-201 has a halflife of 3.044 days, so the effective halflife for 63% of the dose is 2.1 days and for 37% is 2.7 days.  I don't know how sensitive your portal monitors are, but the usual administered activities are 2-4 mCi.  This ought to give you all the information you need to figure out whether 30 days is too long, presuming you know the minimum detectable activity of Tl-201 for your monitor.

Ciao, Carol

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