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

M icrospheres 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 tu mors 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 yttriu m 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 ato mizing pressure of 0.05 M Pa. When the microspheres were heated at 1100oC for 1 h, they precipitated Y-containing crystals such as yttrium phosphate (YPO4), yttriu m o xide (Y2 O3), yttriu m polyphosphate (Y(PO3)3) and yttriu m 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 treat ment. 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.