Interstitial brachytherapy of primary brain tumors

Abstract

Ten patients harboring inaccessible, slow-growing or recurrent malignant primary brain tumors were treated by the stereotaxic implantation of a radionuclide seed, 192Ir or 198Au, either permanent or removable. The strength for 192Ir seeds was selected to deliver 10,000-12,000 rads to the periphery of the tumor and that for 198Au seeds to deliver 4000-7500 rads. Of the 6 patients treated with 192Ir, 3 showed objective responses lasting 8, 11 and 12 mo., respectively; 1 patient''s disease stabilized for 18 mo. Of the 4 treated with 198Au, 3 showed responses lasting 5 mo., 6 mo. and 2 yr, respectively. Because of the higher dose rate attainable with 198Au, removable implants of this material are more effective against the faster-growing malignant tumors. Another radionuclide, 125I, is being tested against brain tumors. The radioactivity of 125I is high but because its gamma emission is less energetic by a factor of 10 than that of 198Au or 192Ir, its radiation field is concentrated within a radius of 2.5 cm or less. This low-energy gamma emission makes it easier to protect medical personnel and patient families against the nuclide when 125I is used.