175Yb-labeled hydroxyapatite:: a potential agent for use in radiation synovectomy of small joints

The preparation of Yb-175-labeled hydroxyapatite (HA) particle is described for possible use as an agent for radiation synovectomy (RS) of small-sized joints. Yb-175 was produced by thermal neutron irradiation of enriched (98.6% in Yb-174) ytterbium target at a flux of similar to 3 x 10(13) n/cm(2)/s for 7 days. Specific activity of 5.5-6.0 GBq/mg and a very high radionuclidic purity to the extent of similar to 100% were obtained. In the work reported herein, HA could be labeled with Yb-175 in very high radiochemical purity (> 99%) using 10 mg of HA particle at pH similar to 7. The radiolabeled particulates showed excellent in vitro stability at room temperature. Serial scintigraphic images of normal as well as arthritis-bearing Wistar rats following intra-articular injection of Yb-175-HA particles in the knee joint showed complete retention of activity within the synovial cavity with no measurable activity leaching out from the joint till 144 h post-injection. (c) 2006 Elsevier Inc. All rights reserved.