Branch of medicine that uses radiation for diagnosis (diagnostic imaging) and treatment (radiation therapy) of disease. Originally, it involved X rays for diagnosis and X rays, and other ionizing radiation for treatment. Diagnostic methods now include isotope scanning (see nuclear medicine), use of non-ionizing radiation, and radio-immunoassay (in which radioactive isotopes in antibodies against hormones detect minute amounts of hormones for diagnosis of endocrine disorders). Radiotherapy now includes, in cancer treatment, radioactive hormones and chemotherapeutic drugs.