I-131 Tx to pregnant patient

[JGarrett@mbhs.org]

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





Jeffrey A. Garrett, MS, DABR

Chief Physicist

Mississippi Baptist Medical Center

1225 North State Street

Jackson, MS 39202



Office: 601-968-1725

Cancer Center: 601-968-1416 or 1420

Fax: 601-960-3317











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