Preparation and bioevaluation of 166Ho labelled hydroxyapatite (HA) particles for radiosynovectomy.

The preparation of 166Ho labeled hydroxy apatite (HA) particles for radiosynovectomy applications is described in this paper. 166Ho was prepared by the irradiation of Ho2O3 at a flux of 1.8 x 10(13) neutrons/cm2/s for about 7 days. The irradiation resulted in the production of approximately 17 GBq of 166Ho activity at the end of six hours post end of bombardment and the corresponding specific activity was approximately 3-4 GBq/mg of Ho. The irradiated target was dissolved in 0.1 N HCl solution. Radionuclidic purity was ascertained by high resolution gamma ray spectrometry. HA particles were synthesized and characterized by X-ray diffractometry. Labeling studies were carried out with and without citric acid as a transchelating agent. Radiochemical yield and purity of the 166Ho-HA particles were ascertained by paper chromatography and by paper electrophoresis techniques. Labeling yield of >98% could be achieved at pH 7, with 40 mg of HA particles and 8.6 microg of Ho. 166Ho-HA particles prepared were stable for 72 h. Bio-evaluation of the 166Ho -HA particles were carried out by injecting approximately 74 MBq dose in 200 microL (approximately 8 mg of 166Ho-HA particles) directly into the arthritis induced knee joints as well as into the healthy knee joints of white New Zealand rabbits. Images of the injected joints of the animals recorded using a gamma camera at regular intervals showed good retention. Blood samples were collected from the animals and activity assayed in a scintillation detector. Experiments were also carried out under identical conditions in normal rabbits. In both the cases, it was observed that there was no significant extra articular leakage of the injected activity over the study period of 96 h post injection.