Determination of RBE of 10 kV and 25 kV X-rays for cell survival and micronuclei induction

The data about relative biological effectiveness (RBE) of low-energy X-rays as well as the RBE dependence on photon energy allow no definitive conclusions about their action on living cells. X-rays in the range ~10 – 50 keV are widely applied in the diagnostic radiology (particularly mammography) and radiotherapy (e. g. brachytherapy). The RBE of 10 kV and 25 kV X-rays relative to 200 kV X-rays by X-ray tube irradiation was determined for cell survival and micronuclei induction in mouse fibroblasts NIH/3T3 and human mammary epithelial cells MCF 12A. The RBE 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. However, the detailed RBE dependence on photon energy can be determined only at a monochromatic X-ray source. A tunable, quasi-monochromatic X-ray source in the energy range 10 – 100 keV based on the channeling of a relativistic electron beam in a diamond crystal is under construction at the ELBE accelerator at Forschungszentrum Rossendorf. 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.