Abstract
Recent studies using the technique of X-ray microplanar beams generated with synchrotron radiation showed that radiobiological effects between normal tissue and tumors were quite different, supposing that it seemed to effectively repair itself in normal tissue but failed to do in tumors. Consequently, the therapeutic index of single-fraction unidirectional microbeam irradiations has been shown to be larger than that of single-fraction unidirectional unsegmented beams. This phenomenon has attraction for a new technique of tumor radiotherapy, but it is still unknown not only biological effect itself but also its mechanism.
This year, we examine the difference in cell-killing effect between normal human and human tumor cells irradiated with X-ray microbeams generated with synchrotron radiation. Cells were irradiated with single-dose-fraction arrays of thin (25µm) planes of microbeams generated at BL28B2 of SPring-8 in Japan Synchrotron Radiation Research Institute, and then detected the cell-killing effect with the colony-formation assay as reproductive cell death. The obtained results show that cell-killing effect in normal human cells used together with a specific inhibitor of gap-junction mediated cell-cell communication, assuming no bystander effect, was lower than that in cells without the inhibitor. On the other hand, there observed no or less difference in tumor cells. The results indicate that the cellular response, involving bystander effect, after X-ray microbeam irradiation is basically different between normal and tumor cells.
