[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Declared pregnancy question



Dear Greg -

Several good comments have been posted already. Let me add some thoughts
about the fetal thyroid dose, from free I-125, after the first 10-12 weeks,
which may be the major concern. The internal dose problem has two issues -
(1) I-125 bound to penicillin (for which I have no knowledge of what the
biological model might be) and (2) free I-125 (NaI). First one must study
the potential for intake. Iodine as NaI is volatile and may be inhaled; I
assume she is working in some sort of hood environment. Once labeled, I
would think chances for intake would be lower and limited to hand-to-mouth
transfers. It is good that this is a conscientious worker, that is in her
favor to limit intakes. In the biological model, the fetus may receive dose
from the mother's organs, but more importantly from activity which may cross
the placenta. Defining all of this for I-125 labeled penicillin may be
difficult; I doubt that there's much published data, and what there is
probably comes from animal studies. If you can find any data, I'd be happy
to work with you to calculate some dose estimates. My guess, however, is
that any such doses will pale in comparison to the fetal thyroid dose from
I-125 NaI which may be taken in by the mother. Dose estimates I recommmend
are:

3 mo    290 mGy/MBq               7 mo    160 mGy/MBq
4 mo    240 mGy/MBq               8 mo    150 mGy/MBq
5 mo    280 mGy/MBq               9 mo    120 mGy/MBq
6 mo    210 mGy/MBq

This is from Evelyn Watson's excellent paper in the 5th Int.
Radiopharmaceutical Dosimetry Symposium. These numbers give dose to the
fetal thyroid per unit activity taken in by the mother. The fluctuation
between 3 mo and 5 mo is due to changing thyroid uptake and mass, competing
to drive the dose higher or lower. After that, changes in mass seem to
dominate.

External sources of exposure, and intakes can be studied as well as models
allow, to look at average dose to the fetus as a whole, but fetal thyroid
dose from potential intakes is certainly a valid concern for this worker,
and may be the most important.



Michael G. Stabin, PhD, CHP
Assistant Professor of Radiology and Radiological Sciences
Department of Radiology and Radiological Sciences
Vanderbilt University
1161 21st Avenue South
Nashville, TN 37232-2675
Phone (615) 322-3190
Fax   (615) 322-3764
e-mail  michael.g.stabin@vanderbilt.edu

"Quantum Mechanics: The dreams stuff is made of"
- Steven Wright

> Subject: Declared pregnancy question
> Message-ID: <sa192af6.035@operations.und.edu>
>
> A head lab tech for one of the med school professors just sent me an
e-mail that she's pregnant.  The lab she's in uses about 1 mCi of I-125
(NaI) per month, about 100 microcuries per procedure (labeling penicillin).
She's always been the most conscientious tech on campus, I have never found
any contamination, and no one in the lab ever had measurable dose.   Still,
she's very worried/upset about possible exposure. She said she read
somewhere that Iodine was particularly bad for pregnant women, but can't
remember where or any details.  Right now there are other people in the lab,
so she doesn't have to handle the material herself, but after spring
graduation all of her help may be gone.  She's been trained on the 6/99
version of RegGuide 8.13 Prenatal Exposure.  I am going to meet with her the
Monday after Thanksgiving. Any advice would be appreciated.
>
> Greg Krause, P.E.
> Director, Radiation  & Chemical Safety
> University of North Dakota
> 701-777-3341
> greg_krause@operations.und.nodak.edu


************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html