Preparation of ceramic microspheres for in situ radiotherapy of deep-seated cancer

Radiotherapy is one of the most effective treatments for cancers. However, external irradiation provides only small doses to deep-seated cancers, and often causes damage to healthy tissues. It has been reported that 20-30μm diameter 17Y₂O₃-19Al₂O₃-64SiO₂ (mol%) glass microspheres are useful for the in situ irradiation of cancers. Yttrium-89 (⁸⁹Y) in this glass can be neutron bombarded to form the β-emitter ⁹⁰Y (half-life=64.1h). When injected in the vicinity of the cancer, such activated glass microspheres can provide a large localized dose of β-radiation. The Y₂O₃ content of the glass in the microspheres is limited to only 17mol%. Chemically durable microspheres with a higher Y₂O₃ content need to be developed. Phosphorus-31 (³¹P) with 100% natural abundance can also be activated by neutron bombardment to form the β-emitter ³²P (half-life=14.3d). Chemically durable microspheres containing a high phosphorus content are expected to be more effective for cancer treatment. We prepared pure Y₂O₃ and YPO₄ microspheres using a high-frequency induction thermal plasma melting technique, and investigated the resulting structure and chemical durability. We successfully prepared smooth, highly spherical polycrystalline Y₂O₃ and YPO₄ microspheres with diameters in the range 20-30μm. Both the Y₂O₃ and YPO₄ microspheres showed high chemical durability in saline solutions buffered at pH=6 and 7. These microspheres are expected to be more effective than the conventional glass microspheres for the in situ radiotherapy of cancer.