The application is drawn to radiolabeled biomolecules and methods for radiolabeling biomolecules with radioactive halogen atoms that minimizes loss of the radioactive halogen due to dehalogenation in vivo, preserves the biological activity of the biomolecule, maximizes retention of radioactivity in cancer cells, and minimizes the retention of radioactivity in normal tissues after in vivo administration. Some such radiolabeled biomolecules comprise a radioactive metal atom in place of, or in addition to the radioactive halogen. The biomolecules have an affinity for particular types of cells and may specifically bind a certain cell, such as cancer cells. Relevant biomolecules include antibodies, monoclonal antibodies, antibody fragments, peptides, other proteins, nanoparticles and aptamers.
