| Περίληψη: | Hypoxia, a partial pressure of oxygen (pO2) below physiological needs, is a limiting factor affecting the efficiency of radiotherapy. Indeed, the reaction of reactive oxygen species
(ROS, produced by water radiolysis) with DNA is readily reversible unless oxygen stabilizes
the DNA lesion. While normal tissue oxygenation is around 40 mm Hg, both rodent and
human tumors possess regions of tissue oxygenation below 10 mm Hg, at which tumor cells
become increasingly resistant to radiation damage (radiobiological hypoxia) (Gray, 1953).
Because of this so-called “oxygen enhancement effect”, the radiation dose required to
achieve the same biologic effect is about three times higher in the absence of oxygen than in
the presence of normal levels of oxygen (Gray et al., 1953; Horsman & van der Kogel, 2009).
Hypoxic tumor cells, which are therefore more resistant to radiotherapy than well
oxygenated ones, remain clonogenic and contribute to the therapeutic outcome of
fractionated radiotherapy (Rojas et al., 1992).
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