Journal Club: Breast milk excretion of radiopharmaceuticals: mechanisms, findings, and radiation dosimetry

The latest installment of the journal club is an older article from JNM but still relevant and looks at the radiation dose to infants from isotopes excreted through breast milk. Breast milk excretion of radiopharmaceuticals: mechanisms, findings, and radiation dosimetry by Stabin and Breitz (J Nucl Med 41, 863-873 (2000)) is more of a review article and summarizes some of the past literature looking at concentrations of various radioisotopes and radiopharmaceuticals excreted in breast milk of female patients undergoing nuclear medicine procedures.

The article starts off with a short discussion on the basic anatomy and physiology of the breast and then goes into a nice concise compilation of breast milk concentrations and infant doses for 25 radiopharmaceuticals. The concentrations of radioactivity in breast milk turns out to be relatively low, but not insignificant except for a few of the usual isotopes, most notably I-131 and Ga-67. Suggested times for how long breast feeding should be stopped for are also given. Table 2 of the paper is probably most useful for anybody who needs to do some dosimetry calculations for physicians or concerned patients.

A good paper to add to the library for any medical or health physicist that finds themselves doing patient dosimetry.

Abstract:

The excretion of radiopharmaceuticals in breast milk is studied to understand excretion mechanisms and to determine recommended breast feeding interruption times for many compounds based on the radiation absorbed dose estimated. A literature review is summarized, providing information on breast milk excretion of many radiopharmaceuticals, including the observed fractions of administered activity excreted and the disappearance half-times. Radiation doses to the infant and to the mother’s breasts have been calculated using mathematical models of the activity clearance into milk, with interruption schedules for the nursing infant derived using a dose criteria of 1 mSv effective dose to the infant. In only 9 of the 25 radiopharmaceuticals considered here is interruption in breast feeding thought necessary. However, in the literature, breast milk concentrations of radiopharmaceuticals and half-times varied considerably between subjects, and individual measurements are encouraged to raise confidence in specific cases. The absorbed dose to the mother’s breast approaches 10-20 mGy (1-2 rad) for a few nuclides, but most doses are quite low. Therapeutic administration of 131I-NaI is a special case, for which the breast dose for a 5550 MBq (150 mCi) administration could approach 2 Gy (200 rad). In this article, these data are discussed, with the aim of assisting others in evaluating the significance of administration of radiopharmaceuticals to lactating women. An example of a sampling scheme and calculation to determine dose for a specific patient is also developed.