Germanium-68

Germanium-68 decays by electron capture with a 270.8-day (about 9-month) half-life, far too long to be imaged usefully itself; its entire clinical role is as the parent bound inside a 68Ge/68Ga generator column, decaying continuously to the 68-minute daughter gallium-68 that is eluted with dilute acid for use in PET tracers such as 68Ga-DOTATATE and 68Ga-PSMA-11. Because the parent's half-life is roughly 5,800 times the daughter's, a single generator loaded with germanium-68 supplies a fairly constant, though slowly declining, stream of gallium-68 for around a year before it needs replacing.

Germanium-68 itself is made almost exclusively by high-energy proton bombardment of a gallium metal target enriched in the stable isotope gallium-69, via the 69Ga(p,2n)68Ge reaction; because commercial-scale generator loadings require tens of gigabecquerels of activity and the reaction needs proton energies of roughly 20-30 MeV over several days of irradiation at high beam current, only a small number of high-energy cyclotron and accelerator facilities worldwide can produce it (an alternative 66Zn(alpha,2n)68Ge route using alpha-particle beams exists but is less commonly used).

That narrow production base is why 68Ge/68Ga generator supply has repeatedly lagged clinical demand: GMP-grade generator lead times ran as long as 18 months in the years before the 2016-2020 approvals of gallium-68 DOTATATE and PSMA-11 PET agents, and a 2017 shortage of germanium feedstock further squeezed availability, prompting the IAEA in 2019-2020 to promote direct cyclotron production of gallium-68 (68Zn(p,n)68Ga) as a way to sidestep the germanium-68 bottleneck altogether rather than solve it. Manufacturers including Eckert & Ziegler subsequently expanded generator manufacturing capacity, and by the mid-2020s most large PET centres have access to either generator- or cyclotron-produced gallium-68, though the underlying germanium-68 production base remains concentrated in a handful of accelerator facilities.