In this communication, we describe the successful encapsulation of Lu-177 into the endohedral metallofullerene (LuxLu3-xN)-Lu-177@C-80 (x = 1-3) starting with (LuCl3)-Lu-177 in a modified quartz Kraschmer-Huffman electric generator. We demonstrate that the Lu-177 (beta-emitter) in this fullerene cage is not significantly released for a period of up to at least one-half-life (6.7 days). We also demonstrate that this agent can be conjugated with an interleukin-13 peptide that is designed to target an overexpressed receptor in glioblastoma multiforme tumors. This nanoparticle delivery platform provides flexibility for a wide range of radiotherapeutic and radiodiagnostic multimodal applications.