[Use of radionuclides in therapy]

In nuclear medicine therapy is based on deposition of certain doses of ionizing radiation in tumors or organ tissues. Regarding their linear energy transfer (LET) values and relative biological effectiveness (RBE), principal radiotherapeuticals are alpha-, beta-, beta/gamma- or electron-emitters. In principle, to achieve the desired therapeutic effect, a particular radionuclide should exhibit adequate physical, chemical and biological properties. However, considerable efforts are required in selecting an optimal radionuclide for a specific application and then, in the development of methods for its routine production.

The paper reviews several aspects of use, properties and production of unsealed radiation sources which are intended to be administered for therapeutic purposes. It covers scientific and practical criteria involved in selecting the radionuclide from medical point of view. The main indications for use of radiotherapeuticals are in oncology and rheumathology. Besides well known, like 32P, 89Sr, 90Y and 131I, several other radionuclides are also listed. Some of them are already in routine use while the others are still under investigation. The main chemical forms of radionuclides and indications are revealed. Particular emphasis is put on the discussion on criteria which a radionuclide should fulfill regarding its physical properties (type, energy, half life, ratio and abundance of the particulate and gamma ray emission). Ideally, they should, together with chemical and biological properties, match with the in-vivo pharmacokinetics and localization of the radionuclide and/or radiopharmaceutical. The trend in modern nuclear medicine is introduction of radionuclides of very specific properties. This, on the other side, opens a question of their availability on the routine basis and at reasonable prices. This matter is also discussed in the present review.

Production of radionuclides for therapeutic purposes (as well as those for diagnostics) is performed either in nuclear reactors or in cyclotrons. Advantages and disadvantages of each production are discussed. The main nuclear reactions for routine production of 32P, 89Sr, 90Y and 131I are given, as well as for production of several other reactor or cyclotron-produced radionuclides. These are, e.g., reactor-produced beta-emitter 169Er, beta/gamma emitters 67Cu, 153Sm, 165Dy, 186Re and electron-emitters 80mBr and 125I. Generators for production of alpha emitters 212Bi and 213Bi are also under development. It can be concluded that, at present, besides 131I, large activities of 32P, 89Sr and 90Y are available on regular basis. For many others, routine availability remains yet to be established.