Re: 131-I and pregnancy

["Gibbs, S Julian" <s.julian.gibbs@vanderbilt.edu>]

As a medical radiobiologist I must take issue with the 
previously posted response to the question: How long should 
a patient wait to become pregnant after 131-I therapy for 
thyroid cancer or hyperthyroidism?
The issue is NOT radiation dose to the fetus.  It is dose 
to the maturing follicle in the ovary.  This dose at the 
time of administration and shortly thereafter is 
substantially greater than the dose later to the embryo 
from radioisotope accumulated in the mother's body. Current 
data suggest that the maturing follicle is almost as 
sensitive as the early embryo.  Therefore, one should wait 
for all maturing follicles at the time of irradiation to 
ovulate.  This interval is open to some question.  One can 
find support for waiting from 1 to 12 months, as has been 
recommended to the questioner.  In any event, the wait 
should be "several menstrual cycles."
Hope this helps.
***********************************************************
S. Julian Gibbs, DDS, PhD               Voice: 615-322-3190
Professor of Radiology                    FAX: 615-322-3764 
Dept. of Radiology & Radiological Sciences
Vanderbilt University Medical Center
Nashville TN 37232-2670 Email:s.julian.gibbs@Vanderbilt.Edu

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