Phosphorus-implanted glass for radiotherapy: Effect of implantation energy

A chemically durable glass that contains a large amount of phosphorus is useful for in situ irradiation of cancers. It can be activated to be a β-emitter with a half-life of 14.3 d by using neutron bombardment. Microspheres of the activated glass that are injected to tumors can irradiate the tumors directly with β-rays without irradiating neighboring normal tissues. In the present study, P⁺ ions in various doses have been implanted into a pure silica glass in a plate form at 200 keV. Almost all the implanted phosphorus is present in the inner region of the glass rather than in the surface region, taking the form of phosphorus colloids for all the doses in the range of 5×10¹⁶-1×10¹⁸ cm^-2. A large number of amorphous phosphorus colloid particles with diameters of 10-150 nm are formed in the silica glass that has been implanted with a dose of 1×10¹⁸ cm^-2; these colloid particles are distributed widely in a layer that is centered at a depth of 200-250 nm. All the investigated glasses hardly release any phosphorus and silicon into water at a temperature of 95 °C, even after 7 d. A silica glass that has been implanted with P⁺ ions at 200 keV with a dose of 1×10¹⁸ cm^-2 is believed to be useful as a radiotherapy glass with sufficient phosphorus content and high chemical durability.