TECHNICAL ADVANCE Irradiation of Mammalian Cultured Cells with a Collimated Heavy-Ion Microbeam

As the first step for the analysis of the biological effect of heavy charged-particle radiation, we established a method for the irradiation of individual cells with a heavy-ion microbeam apparatus at JAERI-Takasaki. CHO-K1 cells attached on a thin film of an ion track detector, CR-39, were automatically detected under a fluorescence microscope and irradiated individually with an 40 Ar 131 ion (11.5 MeV/nucleon, LET 1260 keV/mm) microbeam. Without killing the irradiated cells, trajectories of irradiated ions were visualized as etch pits by treatment of the CR-39 with an alkaline-ethanol solution at 378C. The exact positions of ion hits were determined by overlaying images of both cells and etch pits. The cells that were irradiated with argon ions showed a reduced growth in postirradiation observations. Moreover, a single hit of an argon ion to the cell nucleus resulted in strong growth inhibition. These results tell us that our verified irradiation method enables us to start a precise study of the effects of high-LET radiation on cells. q 2005 by Radiation Research Society