A nonradioactive glass in particulate form adapted for radiation therapy in a mammal comprise a biodegradable rare earth-lithium borate glass material of a specified composition which, upon being subjected to an effective amount of neutron irradiation, will produce a beta or gamma emitting radioisotope, the radioisotope being distributed throughout the glass material, the glass upon being introduced into a body fluid for radiation therapy being adapted to react therewith causing the radioisotope to form an insoluble compound on the surface of the glass material which is retained in the glass material and thereby prevented from escaping from the treatment site. Radioactive glasses and methods for carrying out radiation therapy with such radioactive glasses are also disclosed
