STAMBP and leukemia: Actinium-225 (t1/2 = 10 d) deposits a high dose of energy (5–8 MeV) over a short range (50–80 μm), producing specific and potent cytotoxicity16 and has been used clinically to treat leukemia with the antibody lintuzumab.17–19 High linear energy transfer α particles are lethal to cancer cells as a consequence of ineffective double-strand DNA repair.20,21 Moreover, in internalizing systems, such as αMSH-PEG-Cy5-C′ dot and Lintuzumab, each 225Ac decay produces several daughters generating three additional α particles able to contribute to cytotoxicity.13