[en] Radioisotopes are used in medicine for diagnostic imaging, in-vivo competitive binding assays, and therapy. For diagnostic imaging, especially computerized tomography, technetium-99m is usually used, because it is readily available form a Mo-99/Tc-99m generator, and produces a low irradiation dose. For PET scanning, carbon-11, nitrogen-13, oxygen-15, and fluorine-18 are used, but one needs an on-site cyclotron and a radiochemical laboratory. The next major breakthrough may be tumour detection by radiolabelled monoclonal antibodies. For in-vivo competitive binding assays, iodine-125 is the radioisotope most often used, but the present trend is not to use radioisotopes at all for this purpose, because of concerns about radiation. Beta emitters such as yttrium-90, phosphorus-32, and iodine-131 are used as unsealed sources for tumour therapy