Ac Actinium

Actinium-225 is an alpha emitter being tested in targeted cancer therapy.

Basic facts

Symbol	Ac
Atomic number	89
Atomic mass	227.02775(no standard atomic weight: the element has no stable isotopes or characteristic natural composition; PubChem lists this isotope mass)
Group	none (actinide series)
Period	7
Block	f-block
Category	Actinide
Standard state	Solid
Discovered	1899

Source: PubChem, Actinium (periodic table data, retrieved 2026-10-19). Group and period follow the standard 18-column periodic table.

Biotech uses & experiments

radiotherapy

prototype radiotherapy 2016

Actinium-225-PSMA-617

Kratochwil and colleagues reported two men with advanced prostate cancer whose PSA fell below measurable levels and whose scans showed complete response after experimental actinium-225-PSMA-617 alpha therapy; dry mouth was the only notable clinical side effect.

As reported in: Kratochwil, Bruchertseifer, Giesel et al. (2016). 225Ac-PSMA-617 for PSMA-Targeted α-Radiation Therapy of Metastatic Castration-Resistant Prostate Cancer. Journal of Nuclear Medicine. doi:10.2967/jnumed.116.178673

Read free · publisher open access

Patents

Search Google Patents for actinium in biological and medical uses: all patents · recent applications (2022+)

A patent is a legal claim, not proof that something works. See the Patents page.