Relationship between dose rate and oxygen enhancement ratio

Born [1] concluded that the D0 values of dose-effect curves from cells irradiated under chronically hypoxic conditions were not much influenced by the dose rate and that the oxygen enhancement ratio was decreased from 3.9 at 3.64 Gy. min-1 to 1.8 at 0.07 Gy.min-1. These conclusions, however, are not supported by properly performed experiments. Comments on the paper by Born [1] are provided and a method of obtaining realistic oxygen enhancement ratios at low dose rates is described.