Hello everyone:
Regarding I131 and breastfeeding, I would like to present some information
I have been gathering.

These are general comments and are not intended to answer the questions
arising from this particular case. I don't think there is enough
information to make a final judgment on whether a mother should wean after
radioactive  I therapy. I do think that given that the regulatory agencies
and the international organizations for radiation protection say "wean" it
will be very difficult to find a doctor willing to evaluate a particular
case. Nevertheless, here goes the information I have.

The International Commission on Radiation Protection (www.icrp.org)
recommends weaning after I131 therapy. Whatever I the baby ingests goes to
the thyroid. Exposure to radioactive I in infancy results in
hypothyroidism. Exposure to radioactive I increases the chance of thyroid
cancer in the baby. Moreover, "age is a factor for exposure to I-131
because of the differences between thyroid doses for children and adults.
The dose to children is much higher than that to adults because the thyroid
mass in children is smaller, and because milk, as the main route of
contamination, is consumed in higher quantities during childhood. For an
equivalent uptake of I-131, a child's thyroid receives a higher radiation
dose because the same amount of energy is deposited in a smaller tissue
mass (more energy per gram = higher dose). For newborns, the thyroid dose
is about 16 times higher than that for adults for the same ingested
radioactivity; similarly, the absorbed dose is about 8 times higher for
children under 1 year old and 4 times higher for children 5 years old."
(http://www.atsdr.cdc.gov/HEC/CSEM/iodine/who's_at_risk.html)

I haven't found anything on restricting breastfeeding due to the mother's
increased risk, and Kika's proposal sounds reasonable from the mother's
point of view (removing the milk frequently to reduce exposure of the
breast tissue). All weaning recommendations are aimed at protecting the
baby from damage to his/her thyroid.

I suppose these recommendations could be reviewed and I found an (older)
paper that states that breastfeeding can be resumed after I131 diagnosis,
it does not make any conclusions on I131 therapy (although there you can
see the difference in order of magnitude for the dose and extrapolate linearly)
http://jnm.snmjournals.org/cgi/content/abstract/29/3/407

The NRC states that for 0.01MBq (0.0004mCi) of I131 "Complete cessation [of
breastfeeding](for this infant or child)" has to be recommended. But then
they qualify this statement with a footnote to the table: "* The duration
of interruption of breast-feeding is selected to reduce the maximum dose to
a newborn infant to less than 1 millisievert (0.1 rem), although the
regulatory limit is 5 millisieverts (0.5 rem). The actual doses that would
be received by most infants would be far below 1 millisievert (0.1 rem). Of
course, the physician may use discretion in the recommendation, increasing
or decreasing the duration of interruption."
<http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1556/v9/index-old.html#_1_234>

A patient aducation site (www.mythiroid.com) states:

"I am breast feeding and I need a radioactive iodine treatment. What should
I do?

The timing of the treatment depends on the type and stage of your thyroid
cancer, and there is no correct fixed answer that suits all patients.
Additional factors that need to be considered include the importance and
benefits of breast feeding, versus the psychological implications of
deferring cancer treatment. Since the majority of well differentiated
thyroid cancers are slow growing, and often surgery alone may be highly
effective initial treatment, it is not possible to state with 100%
certainty that all women should stop breast feeding immediately to have
radioactive iodine treatment. This decision should be discussed with your
physician. As traces of radioactive can linger for days to weeks in breast
milk, the advisability and timing of reinstitution of breast feeding after
radioactive iodine treatment should also be discussed with a physician."

So, with the limitation of dose to the baby (0.1mSv) and a knowledgeable
person willing to make calculations based on mother's I intake, transfer
factor to milk (available) and effective half life in mother's body (also
available) it should be possible to estimate on a case by case basis when
breastfeeding could be resumed. It is likely to be many weeks.

I hope this information is helpful.

Best regards,

Veronica Garea (ME Nuclear Engineering, PhD Engineering Physics, Nuclear
Safety)
Grupo de Apoyo a la Lactancia Materna de Bariloche
IBFAN Bariloche - LLL Argentina









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