Determination of RBE of low-energy X-rays at ELBE

The precise determination of the relative biological effectiveness (RBE) of low-energy X-rays is important because of their wide application in diagnostic radiology (particularly mammography) and radiotherapy (e. g. brachytherapy). The RBE of both 10 kV and 25 kV X-rays relative to 200 kV X-rays by X-ray tube irradiation was found to be in the range from 1.0 to 1.4, depending on the used
radiation quality, cell line and the biological endpoint. In order to study in detail the RBE dependence on photon energy, the investigations will be continued at a monochromatic X-ray source. The installation of an intensive, tunable, quasi-monochromatic source in the energy range 10 - 100 keV is currently under progress at the ELBE accelerator at Forschungszentrum Rossendorf. X-rays are produced by channeling of a relativistic electron beam in a diamond crystal. The status of the commissioning of the radiation source will be presented, such as the experimental verification of the theoretical calculation of the spatial energy and intensity distribution. Furthermore, a monochromator, designed to minimize the contribution of the background radiation to the dose in the cell target, will be presented.