Scandium-44

Scandium-44 decays with a 3.97-hour half-life and an unusually high positron branching ratio of about 94%, giving PET image quality that compares favourably with gallium-68 while lasting roughly three times as long, long enough for regional distribution from a centralised production site rather than only local cyclotron use. Its chemistry closely resembles that of lutetium-177 and other trivalent lanthanide-like therapy metals, so DOTA-chelated scandium-44 tracers have been explored as a pre-therapy dosimetry match for 177Lu-labelled radioligands such as PSMA-617, an alternative to using 68Ga for the diagnostic scan when a metal-matched surrogate is preferred.

It is produced on a medical cyclotron via 44Ca(p,n)44Sc on an enriched calcium-44 target (natural abundance only about 2%, so enrichment adds cost), or via a 44Ti/44Sc generator in which the long-lived (60.4-year) parent titanium-44 supplies scandium-44 on an ongoing basis without a cyclotron, analogous to a 68Ge/68Ga generator.

Scandium-44 is also discussed as the diagnostic half of a prospective 44Sc/47Sc theranostic pair, since 44Sc and the beta-emitting therapy isotope scandium-47 are chemically identical, but as of the mid-2020s this pairing remains in early clinical and preclinical research rather than routine practice, and 47Sc production has not yet reached clinical scale.