One of the most common approaches in cancer treatment is the removal of the diseased parts, however unfortunately recovery or return of full function is seldom achieved. Non-invasive treatment techniques where only the cancer cells are destroyed were introduced in mid 80’s. In 1987, microspheres of 17Y2O3-19Al2O3-64SiO2 (mol%) glass, 20-30 µm in diameter were shown to be effective for in situ radiotherapy of liver cancer. 89Yttrium in this glass is non-radioactive but can be activated by neutron bombardment, to 90Y, which is a β-emitter with half life of 64.1 h. They are usually injected into diseased liver through the hepatic artery, and entrapped in small blood vessels, which block the blood supply to the cancer and directly irradiate the cancer with β-rays.

Since the β-ray transmits living tissue only 2.5 mm in diameter and the glass microspheres have high chemical durability, the surrounding normal tissue is hardly damaged by the β-rays. These glass microspheres are already clinically used in Australia, Canada and U.S.A. The content of Y2O3 in the microsphere is, however, limited to only 17 mole%, as they are prepared by conventional glass melting techniques. Recently, Kokubo et al. successfully prepared pure Y2O3 polycrystalline microspheres 20 to 30 µm in diameter by high-frequency induction thermal plasma melting technique, (Figure 1). It was reported that they observed higher chemical durability than the Y2O3-containing glass microspheres. It was further reported that these ceramic microspheres are more effective for in situ radiotherapy of cancer.