Microspheres made of solid glass are used in radiation therapy, wherein the radiotherapeutic radionuclide must be generated in the glass by neutron activation. Microspheres of this type have a high radioactive load, are relatively heavy and contain additional non-therapeutic radionuclides. Additionally, radioactive microspheres made of plastic are used, which can be loaded with radionuclides by chemical means. These microspheres have a lower loading capacity, no additional radionuclides, and are lighter. The therapeutic radionuclide in both cases is Y-90. Microspheres made of nanoporous glass contain the therapeutic radionuclide, have a high loading capacity, require no neutron activation, can be parallel charged with multiple therapeutic and with diagnostic radionuclides, and are very light. It is possible to produce them in a radiochemical laboratory. Microspheres of this type can also be used diagnostically in preparation for therapy. For this purpose, they can be provided in a therapeutically or diagnostically specified quantity and radioactivity.