Ionizing radiation from actinium-225 decay

Ionizing radiation from actinium-225 decay consists predominantly of high linear energy transfer (LET) alpha particles emitted by 225Ac and its short‑lived daughter nuclides, which collectively release multiple alpha emissions per decay event and deposit energy over a short tissue range of roughly a few cell diameters, causing dense ionization tracks and efficient induction of DNA double-strand and clustered breaks that kill targeted cells while limiting cross-fire to adjacent tissues when properly delivered via a targeting vector in targeted alpha therapy[4][6][7][8][9]. Actinium-225 has a half-life of about 9.9–10 days and functions as an in vivo alpha generator; its decay chain produces several daughter radionuclides (including 221Fr and 213Bi) whose emissions contribute to therapeutic effect and provide useful gamma lines (e.g., ~440 keV from 213Bi) for imaging and quality control[5][7][9]. Therapeutically, 225Ac is conjugated to antibodies, peptides, or small molecules (e.g., PSMA ligands, girentuximab for CAIX), enabling selective delivery of alpha radiation to cancers such as metastatic castration-resistant prostate cancer and clear-cell renal cell carcinoma, among others explored in neuroendocrine tumors, glioma, bladder cancer, and leukemia[2][3][6][8]. While highly potent, clinical implementation requires attention to daughter redistribution, organ-specific toxicities (notably salivary and renal), hematologic effects, production and purity constraints, chelation stability, and accurate dosimetry due to the steep biological effectiveness of high-LET alpha radiation[3][6][8][9][10].

Other names

Alpha-particle radiation from actinium-225Alpha emissions from 225Ac decayTargeted alpha therapy radiation from actinium-225225Ac decay radiation

High linear energy transfer (LET) alpha-particle–induced dense ionization causing DNA double-strand and clustered DNA breaks leading to cytotoxicity in targeted cells[3][6][8] - Short tissue range of alpha particles (on the order of a few cell diameters, tens of micrometers) concentrates dose within targeted lesions while limiting cross-fire to surrounding tissue[4][6][8][9] - Multiple alpha emissions per 225Ac decay via daughter nuclides increase local lethality when the radionuclide is internalized in target cells[1][3][7][8]