Stereotactic interstitial irradiation for the treatment of brain tumors
Eighteen patients harboring untreated, inaccessible, slow-growing tumors or recurrent malignant primary or metastatic brain tumors were treated by the stereotactic implantation of permanent or removable radioactive seeds (192Ir, 198Au, 125I). Seed strength was selected to deliver 10,000-12,000 rad to the tumor's periphery for 192Ir, 9000-12,000 rad for 125I, and 4000-7500 rad for 198Au. Three of six patients implanted with 192Ir seeds had objective responses for 2, 8, and 12 months, and a fourth stabilized for 20 months. Five of 9 patients treated with 198Au were evaluable, three of whom responded for 3, 5, and 20 months. Two patients who received 125I have been evaluated to date and are early failures. Two patients who received 125I have been evaluated to date and are early failures. Because of its higher dose rate 198Au is superior for the faster-growing malignant tumors; but because 125I is easier to shield, 125I seeds with greater activity are being developed for evaluation.