Production of microspheres labeled with holmium-166 for liver cancer therapy: the preliminary experience at IPEN/CNEN-SP

Microspheres labeled with therapeutic radionuclides for malignancies of liver are widely used in many countries. The internal radionuclide therapy uses a permanently implanted device, such as TherasphereR or SIR-SpheresR, or a biodegradable device that provides structural support for the radionuclide of choice and causes the tumor reduction. Three different types of material supports have been investigated, i.e., biodegradable polymer-based, glass-based and resin-based microspheres. Nowadays there is a project concerning the labeling of these 3 materials with 166Ho being developed at IPEN-CNEN/SP and coordinated by the Radiopharmacy Directory. 166Ho(t1/2=26.8 h) is a beta minus emitter (Emax=1.84 MeV), with right properties for radiotherapy and can be produced with the low power Brazilian Nuclear Reactor IEA-R1m. The aim of this work is to describe the stage of development of this project. The initial experience used resin-based microspheres, a cation exchange resin labeled with 166Ho, it showed the essential characteristics for liver therapy. Preliminary results of the preparation of glass-based microspheres labeled with 165Ho showed that 5% of Ho2O3 was incorporated in an aluminosilicate glass, through the process of spheronization by flame, which produced spherical microspheres with 20-40μm particle size. The preparation of biodegradable material, polymer-based microspheres, is in its initial stage and the objective is to prepare and label with 165Ho different polymer-based microspheres. These combined efforts have been done to offer a national radiotherapeutic product for the the Brazilian nuclear medicine community at fair value and also to offer a viable possibility of treatment for patients affected by liver malignancies. (author)