111In

Indium-111 (111In) is a radioisotope of indium used in diagnostic nuclear medicine. It is produced in nuclear reactors and decays by electron capture to cadmium-111, emitting gamma radiation suitable for external detection. The most significant emissions are gamma rays with energies of 171 keV and 245 keV, enabling imaging with gamma cameras and SPECT. Its physical half-life is about 2.8 days, allowing imaging over several days after administration.

Indium-111 is supplied in various chemical forms, most commonly indium-111 chloride, indium-111 oxinate, and indium-111 pentetate (DTPA). These forms are used to label different biological targets: In-111 oxinate complexes label white blood cells for infection imaging; In-111-labeled antibodies or peptides are used for tumor imaging and biodistribution studies; In-111 DTPA is used for blood-pool and renal imaging in some protocols.

Applications: The principal clinical use is gamma camera imaging of radiolabeled cells or molecules to study infection and inflammation, including osteomyelitis and inflammatory processes. It has also been used for lymph node mapping in cancer and for tumor imaging with radiolabeled antibodies or peptides. In-111 is compatible with SPECT imaging, providing three-dimensional functional information.

Safety and handling: Like other radiopharmaceuticals, In-111 requires appropriate regulatory oversight, radiation safety practices, and patient-specific dosing. Procedures emphasize minimizing radiation exposure to staff and patients, using proper shielding, and following standards for preparation, administration, and disposal.