Indium-111; 111-In

Indium-111 (111In) is a radioactive isotope of indium that emits X-rays. Its radiological elimination half-life is 67.2 hours (2.8 days). Various substrates can be labeled with Indium-111 for different diagnostic studies: 

• It is combined with pentetic acid (pentetate) is used intrathecally in diagnostic studies of the Cerebrospinal Fluid.
• Leukocytes labeled with Indium-111-hydroxyquinoline, Indium-111-oxyquinoline or Indium-11-oxine are used for localization of inflammatory lesions: abscesses, infections and inflammatory bowel disease. Platelets are similarly labeled.
• Indium-111 bleomycin has been administered by intravenous injection for tumor detection. 
• Indium-111 pentetreotide and the combination with octreotide is used for the detection and localization of tumors of neuroendocrine origin.
• Monoclonal antibodies such as capromab pendetide, ibritumomab tiuxetan, altumomab pentetide, imciromab pendetide and satumomab pendetide have been labeled with indium-111 for detection of malignancies and localization of myocardial infarction.

Some indium-111 compounds such as octreotide are not absorbed by the gastrointestinal tract, so even if they reach breast milk they would not be absorbed by the infant.

Note: 1 mCi (millicurie) = 37 Mbq (megabecquerel)

Waiting times for breastfeeding after radionuclide administration to limit exposure to a maximum of 1 mSv (the average natural radiation received is 6.2 mSv each year.): (Hale, ARSAC 2024, IAEA 2018) 

• Indium-111-CYT-356 (ProstaScint), dose of 5-17 mCi: 14 days.
• Indium-111-DTPA (Cisternogram), 0.5-1.5 mCi dose: 14 days
• Indium-111-DTPA (CSF-cisternogram, shunt patency) dose up to 0.5 mCi: 1 week
• Indium-111-leukocytes, dose from 10 to 18 Mbq: 0 hours ^{(Hale, ARSAC 2024, Mattsson 2021, ICRP 2008)} or 6 - 7 days ^{(ACMUI 2019, US.NCR 2016)}
• Indium-111-octreotide, 0 horas ^{(Mattsson 2021, ICRP 2008)}, 100–200 MBq dose : 60 h ^{(ARSAC 2024, IAEA  2018)} or 6 days ^{(ACMUI 2019)}  
• Indium-111-pentetriotide (OctreoScan), dose 6 mCi: 72 h (3 days)
• Indium-111-santumomab pendetide (OncoScint), dose 4-6 mCi: 14 days

In case of doubt, milk radioactivity can be measured at a nuclear medicine center until measurements on milk samples demonstrate that it is safe to restart feeding. ^{(ARSAC 2024, Stabin 2000)}

If it is desired to completely limit (to 0 mSv) infant exposure, the passage of 5 radioactive half-lives (14 days) will have to be awaited. For leukocyte-labeled Indium-111, 1 day is sufficient.

If the mother has expressed and stored milk prior to the test, she may give it to the infant during the lactation break period. During the interruption period, the milk should be regularly expressed as completely as possible and either discarded or frozen and stored appropriately ^{(ARSAC 2024)}. This stored milk will be fit for consumption after 10 T ½ (30 days) when the radioactivity will have completely disappeared.