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The OER 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, OER may be presented in terms of hyperoxic environments
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is the oxygen fixation hypothesis which postulates that oxygen permanently fixes radical-induced DNA damage so it becomes permanent. Recently, it has been posited that the oxygen effect involves radiation exposures of cells causing their mitochondria to produce greater amounts of reactive oxygen
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and higher relative biological effectiveness (RBE) have a lower OER in mammalian cell tissues. The value of the maximum OER varies from about 1–4. The maximum OER ranges from about 2–4 for low-LET radiations such as X-rays, beta particles and gamma rays, whereas the OER is unity for high-LET
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Barendsen GW. The relationships between RBE and LET for different types of lethal damage in mammalian cells: biophysical and molecular mechanisms. Radiation Res. 1994; 139:257-270.
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Richardson RB and Harper M-E. Mitochondrial stress controls the radiosensitivity of the oxygen effect: Implications for radiotherapy. Oncotarget. 2016; 7:21469-83.
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In solid tumors the inner parts become less oxygenated than normal tissue and up to three times higher dose is needed to achieve the same
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Thoday JM and Read J. Effect of oxygen on the frequency of chromosome aberrations produced by X-rays. Nature, 1947;160:680-609.
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Eric J. Hall and Amato J. Giaccia: Radiobiology for the radiologist, Lippincott
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The maximum OER depends mainly on the ionizing density or LET of the radiation. Radiation with higher
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Ewing D. The oxygen fixation hypothesis: a re-evaluation. Am J Clin Oncol. 1998; 21:355-361.
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207:{\displaystyle OER={\frac {Radiation\,dose\,in\,hypoxia}{Radiation\,dose\,in\,air}}}
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and/or with altered oxygen baseline, complicating the significance of this value.
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