Preparation of phosphorus-containing silica glass microspheres for radiotherapy of cancer by ion implantation

Abstract

A chemically durable glass microsphere containing a large amount of phosphorus is useful for in situ irradiation of cancers, since they can be activated to be a β-emitter with a half-life of 14.3 d by neutron bombardment. When the activated microspheres are injected to the tumors, they can irradiate the tumors directly with β-rays without irradiating neighboring normal tissues. In the present study, P⁺ ion was implanted into silica glass microspheres of 25 μm in average diameter at 50 keV with nominal doses of 2.5×10¹⁶ and 3.35×10¹⁶ cm⁻². The glass microspheres were put into a stainless container and the container was continuously shaken during the ion implantation so that P⁺ ion was implanted into them uniformly. The implanted phosphorus was localized in deep regions of the glass microsphere with the maximum concentration at about 50 nm depth without distributing up to the surface even for a nominal dose of 3.35×10¹⁶ cm⁻². Both samples released phosphorus and silicon into water at 95 °C for 7 d. On the basis of the previous study on P⁺-implanted silica glass plates, the silica glass microspheres containing more phosphorus which is desired for actual treatment could be obtained, without losing high chemical durability, if P⁺ ion would be implanted at higher energy than 50 keV to be localized in deeper region.