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  • Radiopharmaceuticals

    I am working in a hospital and we're working on developing a policy about Radiographic procedures and breastfeeding. I'm wondering about the NRC information about I-131 NaI, I-125 NAI and I-123 OIH. The NRC chart recommends a complete cessation of breastfeeding. So does that mean that the mother can't breastfeed at all anymore? Wouldn't the radiation leave her body at some point and she could resume?

    I have found this further information from NRC:
    Complete cessation was suggested for 67Ga-citrate, 123Isodium iodide, and 131I-sodium iodide. The recommendation for 123I was based on a 2.5% contamination with 125I, which is no longer applicable.

    So does that mean they no longer recommend complete cessation for 123I?

    I have heard that it may make a difference based on whether or not the mother's thyroid was removed, is that true? Can you please give us some guidance about this? Thank you.

  • #2
    I am away from the office this week, but I'm eager to address this issue when I get back. I've recently done a lot of work in this area and I think I can provide you with at least some of the answers you need.

    -James Abbey, MD


    • #3
      I'm back.

      The information that forms the basis of our recommendations comes from the NRC, the International Commission on Radiological Protection (ICRP), and several independent authors such as P.J. Mountford. The NRC's position on these matters is summarized in Regulatory Guide 8.39 (linked at the bottom) which was published in 1997 but reaffirmed by the committee in 2011. This is the document containing their most current recommendations.

      The NRC explicitly recommends the following periods of breastfeeding cessation after administration of Ga-67. Doses are expressed in mCi (1 mCi = 37 MBq).

      <0.2 mCi: 7 days
      0.2-1.3 mCi: 14 days
      >1.3 mCi: 30 days

      In addition, we recommend that the mother try to minimize close contact (<10 cm) with the baby for the same period to reduce the risks of radiation exposure through the body wall. In practice, this means no co-sleeping, no carrying the baby in a sling, having someone else bathe the child, etc.

      The NRC and ICRP statements about the iodine radioisotopes are less straightforward. The mother's current iodine stores, the state of her thyroid, and her surgical history on her breasts all make a difference in the BIOLOGICAL half-life of the iodine atom. This can also be affected by the use of carrier molecules such as hippuric acid. However, the RADIOACTIVE half-life of the iodine is constant regardless of all of these other things. That means that a worst-case scenario of zero biological clearance of the radiation still has a practical endpoint around 5 radioactive half-lives.

      The goal of any breastfeeding policy should be to limit the infant's effective dose of radiation to <1 mSv for the entire procedure, including exposure via both contaminated breastmilk and close-proximity contact with the mother. Calculating the exact radiation dose to the infant is nearly impossible, hence the very low safety cutoff.

      The best approach is to directly measure radioactivity in serial breastmilk samples and interrupt breastfeeding until levels return to baseline. Close contact restrictions can be informed by direct measurements of radioactivity at the patient's skin. Your nuclear medicine facilities may be unable or unwilling to do this.

      The second-best approach is to estimate the cessation period from patient-specific calculations using formulae published in Appendix B of Regulatory Guide 8.39. These calculations try to account for the patient's thyroid status and her living situation. If the predicted period of breastfeeding interruption is long enough that the patient is unlikely to resume breastfeeding at all, some authors suggest that lactation should be suppressed for several days prior to administering the radioisotopes. Iodine concentrates in lactating breast tissue and the gamma radiation exposure increases the risk of breast cancer by around 0.3%.

      The third-best approach is to interrupt breastfeeding for 5 radioactive half-lives. It is our opinion that additional safety gains beyond this point are minimal. This is also the answer to your question about whether the radiation would "leave her body at some point." The advantage of this approach is that you don't have to consider biological clearance, carrier molecules, conjugate forms, thyroid status, or any of the rest of that. The disadvantage is that it is extremely conservative, erring on the side of safety rather than finding the right balance between radiation risks and breastfeeding benefits.

      I-123: Half-life of 13.2 hours x 5 = 66 hours interruption
      I-125: Half-life of 59.4 days x 5 = 297 days interruption
      I-131: Half-life of 8 days x 5 = 40 days interruption

      Please post again or send me a private message if you have any follow-up questions. I'd also like to know how your policy comes out in the end.

      -James Abbey, MD


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