Progress in Target Irradiation of Individual Cells using Focusing Heavy-ion Microbeam

Localized irradiation of specific regions within organisms using heavy-ion microbeam systems provides an attractive means of investigating the mechanism of heavy-ion radiation action. Therefore, we had developed the heavy-ion collimating microbeam system at TIARA of the Japan Atomic Energy Agency (JAEA), and utilized for analyzing heavy-ion induced biological effects. However, there is a difficulty in generating finer beam that is capable for carrying out precise subcellular irradiation in our current system, because of inevitable scattering of ions at the edge of micro collimator. Therefore, we installed new focusing microbeam system at another vertical beam line of AVF cyclotron of TIARA, JAEA. New system can focus heavy-ion beam to minimum 1 µm in vacuum using a quadruplet quadrupole lens system, and equipped with an X, Y beam scanner for fast hitting of single ion to micron scaled samples. To irradiate this finer microbeam to the specific region of individual cells, a cell targeting system, which equipped with a full-automatic inverted microscope and the set of automatic stages, was designed and installed under the beam extraction window. The position of focusing microbeam was detected under microscopic view using plastic scintillator film. The ions irradiated to the sample were detected by solid state ion detector installed on the objective revolver of the microscope, and counted by counter NIM module to control a fast beam shutter. Using the system, irradiation of HeLa cells which was stained with CellTracker Orange fluorescent dye and inoculated on ion track detector CR39 film of 100 µm thick, were carried out.