The application of charged-particle microbeams in radiobiology

For radiobiological applications, the strength of the microirradiation technique lies in its ability to deliver precise doses of radiation to selected individual cells (or sub-cellular targets) in vitro. There is particular interest in studying the risks associated with environmental exposures to α-particle emitting isotopes (which are predominantly due to single-particle effects) and for investigating the so-called 'bystander effect' where non-irradiated cells are seen to respond to signals from nearby irradiated cells. The Gray Cancer Institute charged particle microbeam is one of only two facilities currently in routine use for radiobiology; although a number other facilities are at various stages of development. To be useful in a radiobiological study, a microbeam facility is required to reliably deliver an exact number of particles to a pre-selected sub-cellular target. Furthermore, the low incidence of some biological endpoints means that a large number of cells may have to be individually irradiated (100,000 cells), therefore some form of automation is essential. Our microbeam uses a 1 μm diameter bore glass capillary to vertically collimate protons, or helium ions accelerated by a 4 MV Van de Graaff. Using3He2+ions, 99% of cells are targeted with an accuracy of ±2 μm, and with a particle counting accuracy 99%. Using automated cell finding and irradiation procedures, up to 10,000 cells per hour can be individually irradiated. © 2002 Elsevier Science B.V. All rights reserved.