Single-cell/single-particle irradiation using heavy-ion microbeams

Heavy charged particles transfer their energy to biological organisms through high-density ionization along the particle trajectories. The population of cells exposed to a very low dose of heavy-ion beams contains a few cells hit by a particle, while the majority of the cells receive no radiation damage. At somewhat higher doses, some of the cells receive two or more events according to the Poisson distribution of ion injections. This fluctuation of particle trajectories through individual cells makes interpretation of radiological effects of heavy ions difficult. Furthermore, there has recently been an increasing interest in ionizing radiation-induced bystander effects'', that is, radiation effects transmitted from hit cells to neighboring un-hit cells. Therefore, we have established a single-cell/single-particle irradiation system using a heavy-ion microbeam apparatus at Japan Atomic Energy Agency (JAEA)-Takasaki to study radiobiological processes in hit cells and bystander cells exposed to low dose and low dose-rate high-linear energy transfer (LET) radiations, in ways that cannot be achieved using conventional broad-field exposures. (author)