Radiation dose dependence of the sensitization by oxygen and oxygen mimic sensitizers

New and old evidence is discussed which suggests that the oxygen enhancement ratio (OER) is decreased at lower radiation doses as compared with that of higher radiation doses. In addition, there is evidence that cells irradiated in severe hypoxia have an impaired ability to recover from sublethal damage. However, there is also contrary evidence to these observations. Thus the suggestions that oxygen is not strictly a dose modifying agent have been controversial from the very beginning. It is hoped that new experimental undertakings currently performed in many different laboratories will resolve these issues as well as explain the controversy which has lasted more than 25 years in this field of radiobiologic research.