The feasibility of 225Ac as a source of alpha-particles in radioimmunotherapy.

This paper proposes the utilization of 225Ac for the alpha-radioimmunotherapy of cancer. The isotope decays with a radioactive half-life of 10 days into a cascade of short-lived alpha- and beta-emitting isotopes. In addition, when indicated by the pharmacokinetic requirements of particular clinical applications, 213Bi, with a radioactive half-life of 47 min, can be chosen as an alternative source of alpha-particles in radioimmunotherapy. This isotope is the last alpha emitter in the 225Ac decay-cascade and can be extracted from a 225Ac source at the bedside of the patient. 225Ac can quasi ad infinitum be obtained from one of its precursors, 229Th, which can be made available by various means. The indications for the use of alpha-particles as an alternative to more traditional classes of radiation are derived from the particle-kinetic characteristics and the radioactive half-life of their source isotope, as well as from the properties of the target-selective carrier moiety for the source isotope. It may be expected that useful applications, complementary to and/or in conjunction with other means of therapy will be identified.