Research on biological effects in low dose region by using synchrotron X-ray microbeam irradiation system

点击翻译按钮获取中文摘要

Risk evaluation of low dose or low dose rate irradiation has been great concern for human societies utilizing modern technologies. In order to study biological effect of low level of radiation such as bystander effects, we have developed a new irradiation system with which radiation can be delivered to each cell individually using monochromatic synchrotron X-rays.Developed system is composed of three parts. The first part is to produce X-ray microbeam, either by a Kirkpatrick Baez (K-B) mirror system to focus the X-ray beam or a high-precision slit system to cut out the beam. The second is an epi-fluorescent microscope equipped with a precise motorized stage, on which the sample dish is fixed and irradiated with X-ray microbeam. The third is a fluorescence image analyzer (computer) with a sensitive CCD camera, which recognizes the target cells and their positions. It also controls irradiation of X-ray beam to the target cells, one by one, automatically. The system has been installed at BL-27B in the Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK) in Tsukuba, Japan. Minimum beam size of 5 μm square is now routinely exploited. Intensity of diffracted X-ray beam at the sample position is about 40 R/sec (ca. 10^4 photons/s in 10 μm square). Positioning accuracy of the targets, coordinates of which are automatically analyzed, are about 1 μm. Preliminary results of biological experiments are summarized as below.1. Corresponding to the size of the microbeam used, localization of γ-H2AX and other response proteins was observed in the nuclei of irradiated mammalian cells.2. Survival fractions of the microbeam-irradiated cells could successfully be obtained. By using the nucleus-averaged dose, the dose survival curve appears to be comparable with the case of wide beam experiments.