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Actinium is a rare, naturally occurring radioactive metal, first identified in 1899 and found in only trace amounts. It is so intensely radioactive that it glows faintly blue. Actinium-225 has a half-life of 10 days, decaying by alpha emission to francium-221.
Actinium-225 is a prized isotope for targeted alpha therapy. Its decay releases multiple alpha particles in a cascade, delivering a high, concentrated dose that is highly effective at destroying cancer cells over a very short range. This potency is a strength, though the recoiling radioactive daughters produced along the chain can detach from the targeting molecule and redistribute, making biodistribution and dosimetry harder to control than for single-decay alpha emitters.
Interest has grown quickly as actinium-225 can be linked to peptides, antibodies, and small-molecule inhibitors. The most advanced example, actinium-225 PSMA-617, is used in clinical trials for prostate cancer, alongside programmes targeting myeloid leukaemia, breast, and other cancers.
Actinium-225 has historically been scarce. Supply from legacy sources is not enough to meet the increasing demand and impurities create significant downstream challenges. Newer routes, including high-energy proton irradiation, are expanding supply rapidly and their lower impurity profile make them more desirable for medical use.
StandardX is developing accelerator-based production to help meet this fast-growing clinical demand.