166Ho-microspheres is a product developed at the University Medical Center of Utrecht (The Netherlands) on the basis of microparticles loaded with 166Ho and sold under the name 166Ho-QuiremSpheres®. These particles are obtained by direct activation of 165Ho pre-loaded poly-L-lactic acid (PLLA) particles (mean diameter 30 µm) using a direct, high-neutron flux from a reactor. The specific activity is limited by the maximum time of irradiation as microspheres degrade under neutron beams above one hour.
This product was filed as a brachytherapy drug and as such still to be considered as a medical device. QuiremSpheres® received CE mark in April 2015.
166Ho-microspheres are analogues of 90Y-microspheres and intended for implantation into hepatic tumors by delivery via the hepatic artery to be used in patients with unresectable liver tumors.