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Re: I-131 dose to pregnant woman
> I've basically no experience in this matter but I was rather struck by
some of
> the numbers in this table. The 2.4 rem (24 mSv, ca. 24 mGy) to the uterus
(and
> therefore foetus?) seems to agree with what others have suggested. I note
> however that the thyroid dose is "only" (quotes indicating my uneducated
> reaction) 2.6 rem, most other organs considered in the program seem to get
> greater doses. Now my limited education includes the thought that iodine
is
> supposed to concentrate in the thyroid and that the purpose of giving
I-131 to
> such a patient is to deliver a dose to the thyroid. The numbers produced
below
> would seem to suggest that in fact it is not very efficient. Why is this
so?
> Anyone care to educate me? (in brief I hope :-) )
In brief, I think the numbers are not very good. The dose to the esophagus
and thymus are inexplicably high, and dose to the urinary bladder is way too
low, as is the dose to the thyroid, as you note. Carol Marcus suggests the
J. Nucl Med article for guidance, and I agree. These are the same numbers
that I referred you to on the RADAR web page. The article gives doses to a
number of organs, with dependence on the degree of hyperthyroidism. The dose
to the uterus is representative of the dose to the fetus in the first few
weeks of pregnancy.
20% thyroid uptake
Urinary Bladder 540 mGy
Ovaries 20 mGy
Red Marrow 40 mGy
Thyroid 200,000 mGy
Uterus 30 mGy
40% thyroid uptake
Urinary Bladder 430 mGy
Ovaries 20 mGy
Red Marrow 50 mGy
Thyroid 400,000 mGy
Uterus 30 mGy
60% thyroid uptake
Urinary Bladder 350 mGy
Ovaries 20 mGy
Red Marrow 70 mGy
Thyroid 550,000 mGy
Uterus 30 mGy
80% thyroid uptake
Urinary Bladder 320 mGy
Ovaries 15 mGy
Red Marrow 90 mGy
Thyroid 660,000 mGy
Uterus 20 mGy
I rounded these to 1 or 2 sig figs, and took a rough average of the "fast"
and "slow" thyroid uptake numbers from Table 2 of the JNM article (if you
want the dose in rads, divide the above numbers by 10). These are just rough
estimates for a given patient, more specific thyroid dose calculations
should be done, but they give you an idea of more reasonable numbers for the
other important organs. I will note, however, that the numbers given in the
JNM article for fetal dose at later stages of pregnancy are not reliable, as
fetal uptake has not been considered. See Health Phys 73(5):756-769, 1997
for better numbers in later pregnancy.
Mike
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) 343-0068
Fax (615) 322-3764
e-mail michael.g.stabin@vanderbilt.edu
internet www.doseinfo-radar.com
----- Original Message -----
From: <Peter.Thomas@health.gov.au>
To: <radsafe@list.vanderbilt.edu>
Sent: Monday, August 19, 2002 8:21 PM
Subject: Re: I-131 dose to pregnant woman
>
>
> Peter Thomas
> ARPANSA
>
>
>
> I took this question to a very knowledgeable colleague who ran the numbers
> through an internal dosimetry program called RSAC using ICRP 39 model of
> the human body this is the info he came up with.
>
> Assuming the dose is in milli curies and NOT micro curies (If micro that
of
> course would reduce the dose by a factor of 1000)
>
> Another caveat is that these doses are to the mother and the fetal tissue
> has not yet differentiated into organ at 1 - 2 weeks of gestation.
>
> I don't think a dose to the mother's uterus warrants a therapeutic
abortion
> |--------------------+--------------------|
> |Organ receiving dose|Dose to organ in REM|
> |--------------------+--------------------|
> | Adrenals | 3 |
> |--------------------+--------------------|
> | Bladder Wall | 2.3 |
> |--------------------+--------------------|
> | Bone surface | 4.8 |
> |--------------------+--------------------|
> | Breast | 6.7 |
> |--------------------+--------------------|
> | Esophagus | 17.1 |
> |--------------------+--------------------|
> | Stomach | 17 |
> |--------------------+--------------------|
> |Small Intestine Wall| 2.5 |
> |--------------------+--------------------|
> | Upper Large | 2.5 |
> | Intestine Wall | |
> |--------------------+--------------------|
> | Lower Large | 2.4 |
> | Intestine Wall | |
> |--------------------+--------------------|
> | Kidneys | 2.5 |
> |--------------------+--------------------|
> | Liver | 2.7 |
> |--------------------+--------------------|
> | Lungs | 5.7 |
> |--------------------+--------------------|
> | Muscle | 6.7 |
> |--------------------+--------------------|
> | Ovaries | 2.3 |
> |--------------------+--------------------|
> | Pancreas | 3.3 |
> |--------------------+--------------------|
> | Red Bone Marrow | 5.2 |
> |--------------------+--------------------|
> | Skin | 4.6 |
> |--------------------+--------------------|
> | Spleen | 3.1 |
> |--------------------+--------------------|
> | Thymus | 17.1 |
> |--------------------+--------------------|
> | Thyroid | 2.6 |
> |--------------------+--------------------|
> | Uterus | 2.4 |
> |--------------------+--------------------|
>
>
> Dear Colleagues;
>
> A 23 year old woman received 14.6 mc I-131 for hyperthyroidism.
> A few days later it became apparent that she had conceived one week before
> receiving the I-131.
>
> In other words the 14.6 mc were given in her 1-2 first weeks of pregnancy.
> She is now 5-6 weeks pregnant.
>
> Should abortion be considered in view of possible damage to the fetus ?
>
> Your fast opinion is very important.
>
>
> Thanks,
>
> Moshe Levita
> Ministry of Health, Israel
>
> mlevita@netvision.net.il
>
>
>
>
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