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Iodine131 (,5II) accumulates in mother's milk at the same levels as "normal" iodine (see Chapter 4.11). Among 31 radionuclides studied for their appearance in mother's milk, 13II had the highest transfer (with 30% of the maternal dose), followed by 45Ca and lJ"Cs (both 20%) and *JSr (10%) (Harrison 2003). In their review on 131I, Simon and co-workers (2002) found a median half-life in milk of 12 hours. When the mother received stable iodine to block her thyroid before administration of1311, the median half-life was 8.5 hours. Peak values were measured after 9 hours. Stable iodine blocks also the 1311 uptake of the breast and the infant's thyroid. In 1996, Bennett summarized the kinetics of many radiopharmaceuticals during breastfeeding, among them iodine and technetium isotopes. It is difficult to decide what dosage of radioactivity is tolerable for the breastfed infant; most authors accept 1 mSv, In the context of the radioiodine contamination after Chernobyl, the German Radiation Protection Commission recommended 500 Bq/1 as a threshold value for infant nutrition and cow's milk (Strahlenschutzkommission 1986). For comparison, about 48 hours after administration of 0.37 MBq sodium-iodide131 for medical purposes, a level of 27 kBq/1 was measured in the breast milk -which is still 50 times of the threshold value mentioned above.

4.14.4 Magnetic resonance contrast agents

The scintillation scans that are done today, primarily with technetium (99mTc), are considered much less problematic compared to iodine isotopes. An acceptable residual dosage of 1 mSv is normally reached with pumping and discarding the milk for 12 hours (Prince 2004, Bennett 1996).

Other radioactive compounds arc used for various specific indications. Gallium-67 is used for bone scanning, and whole body scans show an affinity for the breast. With a half-life of 78 hours for the radiation and 9 days for the gallium ion, interruption of breastfeeding is suggested based on the initial dose. Thus, a dose of 0.2 mCi (7.4 MBq) would require a week's cessation of breastfeeding, and 4mCi (148 MBq) would require a month.

Thallium-201 is unique in its affinity for the ischemic myocardium, and is used to delineate this lesion; 85% appears in the heart muscle on the first pass, and only 5% is left in the plasma in 5 minutes. The radioactive half-life is 73 hours; however, it takes 10 days to clear the thallium ion. It has been studied in a lactating woman given 3mCi (llmBq) for a brain scan. In 4 hours the milk level was 8.8 mCi (326 Bq/ml), and in 72 hours it was 2.4 mCi (87 Bq/ml). If the infant had consumed the milk, the dose would have been less than the NCRP radiation safety guidelines (Stabin 2000).

WFDG (2-fluoro-2-deoxy-D-glucose) is used for positron-emission-tomography (PET), and appears in the lactating breast (Shor2002).

Recommendation. The diagnostic or therapeutic use of radiopharmaceuticals, mostly technetium or iodine isotopes, should be postponed until breastfeeding has come to an end. With indications that cannot be postponed, breastfeeding should be interrupted depending on the isotope used and its dosage. If the radioactivity of the milk can be measured simply, then a decision regarding the length of time for which pumped milk is required can be made based on the clearance of radiation from the milk and specifics of the case.

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New Mothers Guide to Breast Feeding

New Mothers Guide to Breast Feeding

For many years, scientists have been playing out the ingredients that make breast milk the perfect food for babies. They've discovered to day over 200 close compounds to fight infection, help the immune system mature, aid in digestion, and support brain growth - nature made properties that science simply cannot copy. The important long term benefits of breast feeding include reduced risk of asthma, allergies, obesity, and some forms of childhood cancer. The more that scientists continue to learn, the better breast milk looks.

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