Upgrading of the gray laboratory soft X ray microprobe and V79 survival measurements following irradiation of one or all cells with a CK X ray beam of different size

The X ray microprobe developed at the Gray Laboratory was originally designed to produce carbon K X rays (278 eV) by electron bombardment and focus them to a few hundred nanometers spot by using a circular diffraction,rating with increasing line density (zone plate), The very fine focus achieved (<0.25 mum radius spot) and the highly localised energy deposition of C X rays (photoelectron range <7 nm), represent unique tools to investigate modern radiobiological phenomena. Recent improvements have been directed to increase the dose rate (up to similar to6 Gy.s(-1) entrance dose averaged over a typical V79 cell) and to evaluate the possibility of using higher energy photons (Al-K of 1.48 keV). The efficiency of the microprobe system has been tested by assessing the clonogenic potential of V79 cells irradiated with C X ray beams of different sizes (5 and 0.25 mum radius) and investigating the relevance of the spatial distribution of cells for the bystander effect.