Structure of Yttrium and Phosphorus-Containing Microspheres Prepared by Spray Dry Method

Microspheres containing yttrium (Y) and/or phosphorus (P) around 25 μm are useful for radioembolization therapy because they are activated to β-emitter by neutron bombardment and infused in blood vessels in the neighborhood of tumors to irradiate β-rays to the tumors. In this study, we attempt to prepare Y and P-containing microspheres by spray drying method. Starting solution containing yttrium nitrate and phosphoric acid in equimolar ratio was spray dried under various conditions. Microspheres 5-30 μm in size are obtained when the starting solution with polyvinyl alcohol (PVA) binder was spray-dried at the atomizing pressure of 0.05 MPa. When the microspheres were heated at 1100oC for 1 h, they precipitated Y-containing crystals such as yttrium phosphate (YPO4), yttrium oxide (Y2 O3), yttrium polyphosphate (Y(PO3)3) and yttrium tetraphosphate (Y2P4O13) but most of them were ruptured. Without the PVA binder, small microspheres around 5 μm in size were formed but their shape remained even after the heat treatment. We found that the atomizing pressure of spray dryer remarkab ly affects the size of microspheres and PVA binder is essential to obtain microspheres around 25 μm, but addition of pH adjuster to starting solution is not essential. This study proposed the criterion of conditions to prepare Y and P-containing microspheres by spray drying method.