Abstract
The detailed mechanism of the bystander response to the radiation of the cells could be studied only with the microbeam irradiation system. Using our synchrotron X-ray microbeam irradiation system, we can irradiate an arbitrarily-defined region as target with desired number of X-ray photons. Using a criterion to distinguish live or dead presented last year, we have measured the survival fractions of cells irradiated with microbeam X-rays.
V79 cells were seeded on the dish in a very low concentration in order to prevent the overlapping of colonies. Targeted cell nuclei were irradiated with 10 µm square X-ray beam (5.35 keV, about 30 R/sec). When targets were irradiated with 200 R, 400 R, 600 R, 800 R and 1000 R, the survival fractions were 62.9%, 51.9%, 22.5%, 15.2% and 13.8%, respectively.
The energy of X-rays is absorbed only by targeted area. In order to compare our results with those in broadbeam experiments, we propose here nuclear-averaged dose, assuming that the cell has a thin double-cylindrical structure; inner cylinder is cell nucleus. Dose-survival curve thus obtained in the microbeam experiments is, almost the same as, or slightly higher than obtained in broadbeam experiments. Considering the difference in the irradiated area, these results may support the idea that damages in cell nucleus are critical to determine the cell death.
