Holmium-166 therapy of malignant and benign diseases.

Abstract

Holmium-166 (Ho-166), one of the lanthanide radionuclides and produced upon neutron irradiation of naturally abundant Ho-165, is an almost ideal radionuclide for therapeutic purposes. The reasons for this are; 1) it is a strong beta emitter (Emax = 1.86 MeV) with maximum range in soft-tissue of 8.4mm, 2) it has a short physical half-life of 26.9 hours, 3) it emits a gamma photon (81 keV, 5.4%) that can be used for external imaging of post-therapy monitoring purpose. Clinical trials of Ho-166 therapy for various malignancies and benign conditions are under way in Korea, 166Ho(NO3) solution is applied into the balloon following percutaneous transfemoral coronary angioplasty (PTCA) in an attempt to inhibit neointimal hyperplasia incident to ballooning injury. Chitosan obtained by deacetylation of naturally abundant Chitin is complexed with Ho-166 by mixing acidic Chitosan solution at a room temperature with higher than 99% labelling yield. The Ho-166 complex is stable in vitro and vivo. Another benign condition, rheumatoid joint disease, is treated by local administration of the agent into the knee joint for radionuclide synovectomy. Malignant conditions being treated with Ho-166-CHICO (Chitosan complex) include cystic brain tumours, malignant ascites and pleural effusion, hepatocellular carcinomas, recurrent melanoma and recurrent rectal carcinomas. Our clinical experience with Ho-166 or Ho-166-CHICO therapy is presented.