Purpose: Intra-arterial administration of particulates labeled with b^- -emitting radionuclides is one of the promising modalities for the treatment of liver cancer. ¹⁶⁶Ho [T_1/2 = 26.9 hours, E_b(max)= 1.85 MeV, Eg =81keV (6.4%)] could be envisioned as an attractive radionuclide for use in liver cancer therapy owing to its high energy emission, short half-life, and feasibility of its production with adequately high specific activity and radionuclidic purity. Hydroxyapatite (HA) particles in the size range of 20–60 were chosen as the particulate carrier due to their biocompatibility and ease of labeling with lanthanides.

Methods: ¹⁶⁶Ho was produced by thermal neutron bombardment on a natural holmium target. HA particles of the desired size range were synthesized, characterized, and radiolabeled with ¹⁶⁶Ho. The biologic behavior of ¹⁶⁶Ho-HA was tested in normal Wistar rats by carrying out biodistribution and imaging studies.

Results: ¹⁶⁶Ho was produced with a specific activity of 5.55–6.48 TBq/g and radionuclidic purity of 100%. HA particles were labeled with ¹⁶⁶Ho with a high radiochemical purity of >99% and good in vitro stability up to 7 days. The biodistribution and imaging studies revealed satisfactory hepatic retention ( ~89% of injected activity after 2 days) with insignificant uptake in any other major organ/tissue.

Conclusions: ¹⁶⁶Ho-HA exhibited promising features as an agent for liver cancer therapy in preliminary studies and warrants further investigation.