The<unk>  <unk>  or oxygen<unk>  effect in radiobiology refers to the<unk>  of therapeutic or detrimental effect of ionizing radiation due to the presence of oxygen. This so-called oxygen effect is most notable when cells are exposed to an ionizing radiation dose. The<unk>  is traditionally defined as the ratio of radiation doses during lack of oxygen compared to no lack of oxygen for the same biological effect. This may give varying numerical values depending on the chosen biological effect. Additionally,<unk>  may be presented in terms of hyperoxic environments and/or with altered oxygen baseline, complicating the significance of this value. : The maximum<unk>  depends mainly on the ionizing density or LET of the radiation. Radiation with higher LET and higher relative biological effectiveness (RBE) have a lower<unk>  in mammalian cell tissues. The value of the maximum<unk>  varies from about 1–4. The maximum<unk>  ranges from about 2-4 for low-LET radiations such as X-rays, beta particles and gamma rays, whereas the<unk>  is unity for high-LET radiations such as low energy alpha particles.
Oxygen enhancement ratio
Oxygenation index
NC ratio
Arteriovenous oxygen difference
Blood–gas partition coefficient
Standardized uptake value
Arterial input function
Diffusing capacity