Hydrothermal synthesis and preliminary cytotoxicity assessment of gadolinium borate nanoparticles for neutron capture therapy

Neutron capture therapy, such as boron neutron capture therapy (BNCT) and gadolinium neutron capture therapy (GdNCT), has been attracting much attention as a next-generation radiotherapy. Nanoparticles containing both boron and gadolinium can accumulate in tumours because of the enhanced permeability and retention (EPR) effect, thereby simultaneously rendering the benefits of BNCT and GdNCT. In this study, we obtained flake-shaped gadolinium borate (GdBO₃) nanoparticles, approximately 80 nm in length and 20 nm in width, by hydrothermal treatment of a solution containing gadolinium chloride, boric acid, and polyethylene glycol at 220 °C for 24 h. These GdBO₃ nanoparticles did not show any serious cytotoxic effect against human umbilical vein endothelial cells over a concentration range of 3–300 µg·mL^–1. The results suggest that GdBO₃ nanoparticles can accumulate in tumours because of the EPR effect and can function as boron and gadolinium nanocarriers for neutron capture therapy. However, further in vitro and in vivo studies are needed for the application of these nanoparticles in neutron capture therapy. Graphical abstract: [Figure not available: see fulltext.]