Microdosimetric characteristics of micro X-ray beam for single cell irradiation

A tabletop micro X-ray beam irradiation system has been developed to study radiation effects on living cells. The microbeam system is composed of a micro focus X-ray tube, a capillary for X-ray guide, an X-ray semiconductor detector for fluorescent X-ray analysis, and an inverted microscope. A beam profile measurement was performed and the size of the focused beam was 10 /spl mu/m in diameter [full-width at half-maximum (FWHM)] with a divergence of 5.1 mrad. The data on the microbeam measurement were approximately in agreement with a simulation of X-ray optical traces for the capillary. In addition, the microdosimetric characterization for single cell irradiation was performed with the beam profile measurement and a photon-electron transport simulation. The maximum of the dose rate for the sample cells set in the system was estimated to be 0.05 Gy/s. In a preliminary experiment, single yeast cells were irradiated with the X-ray microbeams, and the data on the survival rate of the cell samples for the X-ray doses were obtained. Then, the microbeam irradiation system is useful to investigate the radiation effects on the living cells.