Re: I-131 Tx to pregnant patient

[John Jacobus <crispy_bird@YAHOO.COM>]

I believe that first (RegGuild 8.36) considers uptake

of I-131 by the fetus/embryo, resulting in both photon

and beta dose.  The second considers dose to the

uterus, not the embryo, for photons.  



I would consider the dose by the second method.  For

one thing, organgensis has not progressed for the

embryo to have a have a functioning thyroid.



--- JGarrett@mbhs.org wrote:

> Dear Rad Safers:

> 

> I was just informed that there was a patient a

> couple of weeks ago who

> received an I-131 treatment for residual thyroid

> disease post

> thyroidectomy. The pregnancy test on the day of the

> therapy was negative.

> However, a few days later, 5 -6, the patient's

> period was late. The

> subsequent serum test demonstrated a positive test

> for pregnancy. I have

> done some initial calculation for the dose to the

> uterus/embryo. The amount

> of I-131 administered was 75 mCi. The calculations I

> have performed are

> given below. My first question is what method would

> yall use since there is

> such a drastic difference between the two methods?

> Thanks for your help.

> 

> NRC Guide 8.36 Radiation Dose to the Embryo/Fetus

> Method

> Dose = I x f1 x DF, where I = initial activity in

> uCi = 75 mCi=75000 uCi,

> f1 is fractional uptake to the blood = 1.00, and DF

> is the dose factor =

> 3.64E-3 rem/uCi

> Dose = (75000 uCi)*(1.00)*(3.64E-03 rem/uCi) = 273

> rem => 273 rads to the

> embryo.

> 

> Using Tabular values from internaldosimetry.com

> Dose to Uterus = 2.2E-01 rad/mCi

> Dose = (75 mCi)*(2.2E-01 rad/mCi) = 16.5 rad to the

> embryo

> . . .



=====

+++++++++++++++++++

"Those who deny freedom to others deserve it not themselves, and under a just God cannot long retain it."

Abraham Lincoln



-- John

John Jacobus, MS

Certified Health Physicist

e-mail:  crispy_bird@yahoo.com



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