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Re: I-131 dose to pregnant woman
My understanding is that iodine concentrates in the thyroid, but only
stays long enough to be metabolized into thyroxin and T-4, hormones that
circulate throughout the body. Residence in the thyroid is long enough
for a diagnostic or therapeutic dose to do what is needed. Maybe others
will correct me if I'm wrong.
Tony Harrison, MSPH
Colorado Dept. of Public Health & Environment
Laboratory and Radiation Services Division
(303)692-3046
tony.harrison@state.co.us
>>> <Peter.Thomas@health.gov.au> 08/19/02 07:21PM >>>
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 :-) )
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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