Host: The Japan Radiation Research Society
Co-host: Asian Association for Radiation Research
Our microbeam irradiation system can deliver a desired number of X-ray photons to an arbitrarily defined target region. We compared the cellular responses of microbeam irradiation with those of broad-field (broadbeam) irradiation.
In broadbeam experiments, 1×105 V79 cells were seeded in a 35 mm dish. The entire plate was irradiated uniformly with 5.35 keV X-rays. Cells were collected by trypsinization and survival fractions were measured with the usual colony assay method. On the other hand, in microbeam experiments, 2×10³ V79 cells were seeded in a specially designed dish for microbeam experiments (Φ 34 mm). The targeted cell nuclei were irradiated with a 10 μm square 5.35 keV X-ray beam. Using the criterion that colonies including more than 30 cells are surviving after 60 hours of incubation, we determined the survival fractions of irradiated cells.
Low-dose hypersensitivity was clearly observed in the dose-survival curves obtained in microbeam experiments. In contrast, the low-dose hypersensitivity was less remarkable in the broadbeam experiments. In broadbeam experiments, the entire cytoplasm, as well as nucleus, was irradiated uniformly with X-rays, while most of the cytoplasm was not irradiated in microbeam experiments. In both experiments, energy deposition in the nuclei was almost equal. These results suggest that the energy deposition in cytoplasm might reduce the cell killing effect in low dose region. We are further analyzing this hypothesis considering the differences in experimental procedures.
