Radionuclides for Radioimmunotherapy: Criteria for Selection

In developing and designing radioimmunotherapy, the selection of the isotope is a major factor. This selection depends on a number of criteria and parameters, affecting usefulness and feasibility. Usefulness is directly related to the radiological performance of the ionising radiation in relation to tissue and its morphology, with a major distinction between the effects of alpha and beta-particles (or rays). Usefulness is also directly related to the pharmacodynamic performance of the isotope-carrier (e.g. antibody) complex, where the proper choice of isotope radiodecay halflife is of major importance. Feasibility depends on availability of the components in the isotope-ligand-carrier complex, and also on convenience and safety aspects in the preparation and the handling of the materials as well as in their application in patients. A comparison is made between the various properties of alpha-emitting isotopes that have been proposed over a number of years, concluding that the combination 225Ac- 213Bi deserves serious further attention.