Physico-chemical characterisation and biological evaluation of 188-Rhenium colloids for radiosynovectomy

The physical characteristics of tin (Sn) and sulphur (S) colloids were determined to assess the formulation with suitable properties. Particles were grouped in three ranges for analyzing their distribution according to their number, volume and surface. The ideal particle size range was considered to be from 2 to 10 microns. Membrane filtration and laser diffraction characterization methodologies were used.While membrane filtration could give misleading data, laser diffraction proportions more reliable results. The Sn colloid showed a better distribution of particle volume and surface than S colloid, in the 2 to 10 microns range. The 188Re-Sn colloid was obtained with a radiochemical purity higher than 95% after 30 minutes of autoclaving. While Sn colloid kit stability was verified for 60 days, the 188Re-Sn preparation was stable in the first 24 hrs. No significant intrabatch variability (n = 3) was detected. Biodistribution and scintigraphic studies in rabbits after intraarticular injection showed relevant activity only in knee, being 90% at 48 hours.The 188Re-Sn colloid is easy to prepare, is stable for 24 hours and shows minimal cavity leakage after intraarticular injection into rabbit knees, suggesting this radiotherapeutical agent has suitable physical properties for evaluation for joint treatment in humans.Radiosynovectomy is a radiotherapy, which has been used for more than 40 years to relieve pain and inflammation from rheumatoid arthritis (RA). It was developed as an alternative to surgical synovectomy [1-3]. The procedure consists in the injection of a beta-emitting radionuclide into the joint capsule [4,5], where it remains in contact with the synovial membrane or synovium. The intraarticular-administered radiopharmaceutical is then phagocyted by the lining cells, which are on the synovial surface. While the radionuclide is decaying the absorbed dose is being given to the synovium.188Rhenium is an attractive radionuclide for radiosynovectomy because of its