Rhenium-188

Rhenium-188 is a high-energy beta emitter (maximum energies of 2.12 MeV, 71.1% abundance, and 1.96 MeV, 25.6%; mean beta energy around 763-784 keV) with a short 16.9-17.0 hour physical half-life and a co-emitted 155 keV gamma (about 15% abundance) that permits gamma-camera imaging, biodistribution and dosimetry studies -- chemically and logistically analogous to technetium-99m.

Its key practical feature is on-demand generator production: 188Re is eluted as carrier-free sodium perrhenate from a tungsten-188/rhenium-188 generator, in which the long-lived parent 188W (half-life 69.4 days) is fixed on an alumina column, much like a molybdenum-99/technetium-99m generator. A single generator can supply daily eluted doses for around six months to a year, making 188Re one of the few therapeutic isotopes that hospitals in resource-limited settings can access without importing short-lived material.

188W itself is made in a high-flux reactor by double neutron capture on enriched tungsten-186, 186W(n,γ)187W(n,γ)188W, at facilities such as the High Flux Isotope Reactor (Oak Ridge, USA), the SM-3 reactor (Russia) and BR2 (Belgium). 188Re-labelled agents (e.g. 188Re-HDD/lipiodol for hepatocellular carcinoma, 188Re-labelled bone and vascular agents) have been used mainly in investigator-led studies and in India and other countries where the generator route lowers cost, but none has reached FDA or EMA approval.