Preparation and pre-clinical study of 177Lu-labelled hydroxyapatite for application in radiation synovectomy of small joints.

AIM: We present in this paper, the preparation and pre-clinical study of 177Lu-labelled hydroxyapatite for the application in radiation synovectomy of small sized joints.
METHODS: 177Lu is an adequate radionuclide for therapy, having ability of simultaneously showing therapeutic effects and depicting images. Both hydroxyapatite particulates and 177Lu were prepared indigenously. RESULTS AND
CONCLUSION: Analysis of the gamma ray spectrum showed the radionuclide purity of 177Lu more than 99%. HA particles were synthesized and characterized by FTIR-ATR and X-ray diffractometry. XRD-Pattern generated by the product indicated that the chief inorganic phase of the sample is hydroxyapatite crystal. FTIR spectrum of HA powder calcined at 800°C for 1h showed all the bands that can be assigned to phosphate and hydroxyl groups in an apatite environment. Ca/P ratio was determined by ICP-OES. The Ca/P ratio of 1.68 determined for HA was about 0.6% above the stoichiometric ratio of 1.67. Particle size distribution pattern was obtained with the help of laser particle size analyzer and results showed that more than 80% of the particles bear the size in the range ideal for radiosynovectomy. 177Lu-labelled hydroxyapatite particulates were prepared with high radiochemical purity and yield. >95% labeling yield was achieved at pH 7. Labeled specie remained stable up to 18 days. In vitro stability >99% remained up to >one half life of 177Lu. Bio-evaluation of the 177Lu-HA particles was carried out by injecting approximate activities of 10 and 5 MBq (in 0.1 mL suspension) as intra-articular injection in the right knee joints of rabbit 1 and 2 respectively. Retention of activity was studied using images of the injected joints with the help of a gamma camera at various intervals. In all images no activity was visible in any organ other than knee joints. The retention of the 177Lu activity was followed for 772 hours (30.01 days). Leakage of activity was also assessed indirectly by estimating the residing time of radiopharmaceutical in the synovium. Half life of 177Lu-HA residing time in the knees was estimated to be 154 hours and 158 hours for rabbit-1 and rabbit-2 respectively. No significant extra articular leakage of the injected activity was observed over a period of one month post injection. Pre-clinical study of 177Lu-labelled hydroxyapatite indicated its potential for application in radiation synovectomy of small joints.