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

低剂量或低剂量率辐照的风险评估一直是利用现代技术的人类社会所关注的问题。为了研究低剂量辐射的生物效应，如旁观者效应，我们研制了一种新的辐射系统，利用单色同步辐射X射线将辐射分别照射到每个细胞上。第一部分是X射线微束的产生，通过柯克帕特里克-贝兹（K-B）反射镜系统聚焦X射线束或高精度狭缝系统切割X射线束。第二个是一个epi-fluorescent显微镜配备了一个精确的电动平台，其上的样品盘是固定的，用X射线微束照射。第三个是荧光图像分析仪（计算机），带有灵敏的CCD相机，可识别靶细胞及其位置。它还自动控制X射线束一个接一个地照射靶细胞。该系统已安装在BL-27 B的光子工厂，材料结构科学研究所，高能加速器研究组织（KEK）在日本筑波。现在常规采用5 μm见方的最小光束尺寸。样品位置处衍射X射线束的强度约为40 R/sec（约100 R/sec）。10 μm正方形中10^4光子/s）。自动分析目标坐标的定位精度约为1 μm。生物学实验的初步结果总结如下。相应于所用微束的大小，γ-H2 AX和其他反应蛋白在受照哺乳动物细胞核中的定位被观察到.可以成功地获得微波照射的细胞的存活分数。通过使用核平均剂量，剂量存活曲线似乎是可比的情况下，宽束实验。

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.