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 20–30 μm 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=64.1 h). 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 17 mol%. 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=14.3 d). 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 20–30 μm. 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.