Lehnert, A., Dörr, W., Lessmann, E. and Pawelke, J. RBE of 10 kV X Rays Determined for the Human Mammary Epithelial Cell Line MCF-12A. Radiat. Res. 169, 330–336 (2008).

The dependence of relative biological effectiveness (RBE) on photon energy is a topic of extensive discussions. The increasing amount of in vitro data in the low-energy region indicates this to be a complex dependence that is influenced by the end point and cell line studied. In the present investigation, the RBE of 10 kV X rays (W anode) was determined relative to 200 kV X rays (W anode, 0.5 mm copper filter) for cell survival in the dose range 1–10 Gy and for induction of micronuclei in the range 0.5–3.6 Gy for MCF-12A human mammary epithelial cells. The RBE for cell survival was found to increase with decreasing dose, being 1.21 ± 0.03 at 10% survival. Considerably higher values were obtained for micronucleus induction, where the RBEM obtained from the ratio of the linear coefficients of the dose–effect curves was 2.6 ± 0.4 for the fraction of binucleated cells with micronuclei and 4.1 ± 1.0 for the number of micronuclei per binucleated cell. These values, together with our previous data, support a monotonic increase in RBE with decreasing photon energy down to the mean energy of 7.3 keV used in the present study.

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