Re: thyroid and TB exposure for a I-131 medical treatment

[carol marcus <csmarcus@ucla.edu>]

At 05:52 AM 10/19/99 -0500, you wrote:
>
>
>Could anyone tell me the total body and thyroid exposure for 22.9 mCi of I-131,
>also I am looking for the biological 1/2 life.
>Is there a web site out there that would perform this calculation?  How about a
>web site with a list of biological 1/2 lives.
>
>
>
>
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Radsafers:

ICRP no. 53 has the data for calculating absorbed dose as a function of per
cent thyroid uptake, which varies enormously (0 - 95%) depending on health
or disease state.  It assumes a biological halflife in the thyroid of 80
days for normal adults.  However, halflives vary enormously in patients with
thyroid disease, and in the presence of different drugs.  On oragraffin, for
example, biological halflife can be a couple of hours.

ICRP no. 53 assumes normal renal function, with a biological halflife of 8
hours for the non-thyroidal iodine.  With increasing renal insufficiency,
this goes all the way up to exceedingly high numbers, with nothing going out
the kidneys and some coming out through stool.  If the patient is on
dialysis, approximately one half to one third of the non-thyroidal iodine
comes out after each of the first few dialyses; that which is in the gut
comes out more slowly.  The transit time for intestinal contents in normal
adults is about three days.

Oak Ridge's MIRDOSE software is fine if you know uptake, halflives, and
thyroid mass for your patient.  There are no "tables" of halflives.  If the
patient is other than "normal" with respect to thyroid disease, and has
other than "normal" iodine intake (stable iodine, that is), the halflife
will have to be measured.

Ciao, Carol

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

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