Fig. 1From: Interfering with Tumor Hypoxia for Radiotherapy OptimizationDirect interaction of ionizing radiation with oxygen: the oxygen fixation hypothesis. (a) Oxygen enhancement ratio (OER). Curves represent the surviving fractions of cells irradiated with increasing doses of ionizing radiation under normoxic (black) and hypoxic (red) conditions. The OER is defined as the ratio of the radiation dose under hypoxia and the radiation dose under normoxia to achieve the same biological effect. (b) The oxygen fixation hypothesis mechanistically describes the role of oxygen for enhanced DNA damage and cell killing under normoxic conditions and includes the initial formation of more ROS and chemical derivatization (“fixation”) of DNA damage in presence of oxygen. See details in textBack to article page