sealed source [ME, seel, mark; Fr, sourdre, to spring] , a source of radioactivity that is permanently encased in a container or bonding material to prevent leakage. Sealed sources, such as seeds, needles, and specially designed applicators, are used in the implantation of cesium-137, iodine-125, iridium-192, radium-226, and other radionuclides for the treatment of various malignant tumors.
