Stability of biodegradable radioactive rhenium (Re-186 and Re-188) microspheres after neutron-activation

Our objective was to determine if microspheres made from the biodegradable polymer poly(lactic acid) that contained rhenium could withstand the condit ions of direct neutron activation necessary to produce therapeutic amounts of radioactive rhenium. The radiation damage of the polymer produced by gam ma -doses of up to 1.05 MGy from Re-186 and Re-188 was examined by scanning electron microscopy and size exclusion chromatography. At a thermal neutro n flux of 1.5 x 10(13) n/cm(2)/s the microspheres melted after 3 h in the n uclear reactor, but suffered little damage after 1 h of radiation and relea sed less than 5% of the radioactivity during incubation in buffer at 37 deg reesC. The radioactive microspheres produced in this manner have a specific activity too low for radioembolization for treatment of liver tumors, but could be injected directly into tumors or applied topically to the wound be d of partially resected tumors. (C) 2001 Elsevier Science Ltd. All rights r eserved.