Samarium-153-particulate hydroxyapatite radiation synovectomy: biodistribution data for chronic knee synovitis

Biodistribution data for the radiation synovectomy agent samarium-153-particulate hydroxyapatite (153Sm-PHYP) are reported.

Mean extra-articular activity accumulation calculated from serial whole-body scans in 13 patients treated for chronic knee synovitis was 0.74% of injected activity (range 0%-3%).

In four patients (31%), activity was noted in the lung (mean 0.68% of injected activity). In six patients (46%), 0.29% of injected activity accumulated in the regional lymph nodes and in three patients (23%), 0.62% of injected dose accumulated in the liver. Absorbed dose estimates were lung: 14 mGy, regional lymph nodes; 50 mGy, liver; 4 mGy. SPECT demonstrated good distribution of 153Sm-PHYP throughout the anterior knee compartments, although distribution to the posterior compartment was variable.

Distribution is dependent on adequate knee flexion immediately following injection and may be influenced by the size range of labeled particles. Favorable biodistribution data suggest that 153Sm-PHYP is a potentially useful radiation synovectomy agent.