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The Science

Why alpha emitters are different.

Targeted alpha therapy (TAT) delivers high-energy, short-range radiation directly to cancer cells via a targeting ligand — combining precision binding with potent, localized cytotoxicity.

Foundations

Radioligand therapy, in one diagram

  1. 01

    Targeting ligand

    A small molecule or peptide that binds selectively to a tumor-associated receptor (e.g. SSTR2, PSMA).

  2. 02

    Linker / chelator

    Covalently joins the ligand to a chelator capable of stably caging the radioisotope payload.

  3. 03

    Radioisotope

    An alpha emitter such as actinium-225 — the cytotoxic payload delivered directly to the tumor cell.

A small molecule radioligand binding to a tumor cell receptor
Alpha vs Beta

Two fundamentally different radiation profiles

Alpha and beta particles differ in mass, energy, and range — with meaningful implications for the patterns of DNA damage they produce.

α

Alpha particles

Particle
Helium nucleus (2 protons + 2 neutrons)
Energy
~5–9 MeV
Range in tissue
~40–100 μm (2–10 cell diameters)
LET
High (~80 keV/μm)
Dominant DNA damage
Clustered, irreparable double-strand breaks
β

Beta particles

Particle
Electron
Energy
~0.5–2.3 MeV
Range in tissue
~1–10 mm (~100–1000 cell diameters)
LET
Low (~0.2 keV/μm)
Dominant DNA damage
Predominantly single-strand breaks

Values are approximate ranges drawn from published radiobiology literature and are shown for educational purposes; actual values depend on the specific isotope.

The isotope

Why actinium-225

Schematic of actinium-225 decay chain

Actinium-225 (Ac-225) is an alpha-emitting radionuclide with a ~9.9-day half-life that decays through a cascade releasing four alpha particles per parent atom — concentrating cytotoxic energy within a few cell diameters of the binding site.

Compared with beta-emitting radioligand therapies, alpha emitters like Ac-225 are biologically more potent per decay, with the potential to overcome hypoxia and cell-cycle dependencies that limit other forms of radiation.

  • ▸High linear energy transfer (~80 keV/μm)
  • ▸Short path length spares adjacent healthy tissue
  • ▸~9.9-day half-life supports centralized supply
  • ▸Cascade of 4 alpha decays per Ac-225 atom