A comparison of cytotoxicity after whole- or partial-cell irradiation with synchrotron-produced ultrasoft X rays

We introduce a method which allows partial-volume irradiation of live cells using synchrotron-produced ultrasoft X rays and micro-fabricated irradiation masks. The masks were made by X-ray lithography at the University of Wisconsin Synchrotron Radiation Center, and they consist of 1.85-mu m-wide stripes of gold 1.35 mu m apart plated onto thin silicon nitride membranes. When placed adjacent to Mylar on which live cells are plated, these masks allow cells to be irradiated in a striped pattern with dimensions much smaller than the cell nuclei. Using 1340 eV synchrotron-produced X rays, we compare the survival of cells subjected to uniform irradiation and cells subjected to partial-volume irradiation, Our results show that, at equal mean dose to the nucleus (i.e. equal total energies deposited), survival is not statistically different for the two treatments over a wide range of doses. Thus imparting equal energies to smaller intranuclear volumes does not appear to enhance cell killing, (C) 1998 by Radiation Research Society.