The goal of targeted radionuclide therapy is to selectively deliver radiation to cancer cells and/or diseased tissue with minimal toxicity to surrounding normal tissues. The basis for successful radionuclide therapy is a theranostic approach that integrates diagnostic testing for the presence of a molecular target for which a specific treatment/drug is intended (Fig. 1). Theranostics is a revolutionary approach that promises improved therapy selection on the basis of specific molecular features of disease, greater predictive power for adverse effects due to improved patient-specific absorbed dose estimates, and new ways to objectively monitor therapy response. Currently, radionuclide therapy remains an important treatment option because ionising radiation from radionuclides can kill cells and inhibit growth in the benign and cancerous lesions that result from proliferative diseases. Radiation kills cells by damaging the DNA in the cell nucleus, thereby inhibiting cellular reproduction. Rapidly developing studies also demonstrate the beneficial effect of combining radionuclide therapy with chemotherapy.