Fig. 6-1 System of target cell irradiation with heavy ion microbeam Two automatic microscopes were used for target cell irradiation. The cells were inoculated in the center area of the cell dish, and their positions were detected by fluorescent staining. Thereafter, the cells were rapidly irradiated with a heavy ion microbeam using pre-detected cell position data. The positions of heavy ion hits were detected without killing cells by etching the bottom of the cell dish. Then the effects of ion hits on cells were observed continuously after irradiation.

Fig. 6-2 Effects of single heavy-ion hit on cells The number of cells per colony was measured 60 hours after irradiation. The cells hit on their nucleus showed strong growth inhibition. On the other hand, the cells hit on their cytoplasm exhibited different hit effects. In addition, the cells co-cultured with heavy-ion hit cells showed limited growth by bystander effect compared with the cells of a non-irradiated sample.

The biological effect of heavy ion beam should be analyzed when utilizing its higher biological effectiveness on cancer therapy and plant breeding. Because target irradiation of heavy ion beam was not able to carry out, it was impossible to analyze the effects of heavy ion irradiation at individual cells. The targeting of cells individually with single heavy ions is a good way to solve this issue. Therefore, we established a method for irradiating individual cells using a heavy ion microbeam apparatus at JAERI-Takasaki (Fig. 6-1). Using this system, Chinese hamster ovary cells were irradiated with an 40Ar13+ beam, after which the effects of irradiation were observed individually. Cells hit by a single argon (Ar) ion on their nucleus showed strong growth inhibition after 60 hours of post-irradiation incubation. In addition, we also observed bystander effect on the growth of non- hit cells that were co-cultured with the hit ones in the same cell dish (Fig. 6-2). This cell targeting system will enable us to analyze the molecular mechanisms of the biological effects of heavy ion beam. We believe that the molecular analysis of the ion- hit effects including the bystander effect will contribute to the development of novel applications of heavy ion beam, such as development of more effective methods for cancer therapy and advanced techniques for ion-beam breeding.

Reference T. Funayama et al., Irradiation of Mammalian Cultured Cells with Collimated Heavy Ion Microbeam, Radiat. Res., 163(2), 241 (2005).

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