The oxygen enhancement ratio (OER) is defined as the ratio of the isoeffect dose to hypoxic cells to that to aerobic cells. OER generally ranges between 2 and 3 for low-LET radiation where the higher the dose the higher the OER.
Hyperbaric oxygen (HBO) serve as radiosensitizer (its use just prior to radiotherapy) and also as a treatment modality for radiation necrosis (e.g., osteoradionecrosis after radiotherapy).
https://www.ncbi.nlm.nih.gov/pubmed/28613568
https://www.ncbi.nlm.nih.gov/pubmed/28126298
The mechanistic underpinnings of the oxygen effects remain incompletely understood, but indirect effects to nuclear DNA are explained above by others. Here I wish to highlight two other potential mechanisms.
A recent study attributed the oxygen effect to radiation-induced effects in mitochondria, such that reactive oxygen species generated in mitochondria target nuclear DNA indirectly.
https://www.ncbi.nlm.nih.gov/pubmed/26894978
Targeted cyctoplasmic irradiation induces DNA damage, inactivates clonogenic potential and causes mitochondrial dysfunction leading to increased oxidative stress. These suggest extranuclear target for radiation effects.
https://www.ncbi.nlm.nih.gov/pubmed/24080278
https://www.ncbi.nlm.nih.gov/pubmed/17575156
https://www.ncbi.nlm.nih.gov/pubmed/10220401
The new study now shows, for the first time, linear energy transfer (LET) dependent changes in the oxygen enhancement ratio (OER) for DNA double strand breaks following X-ray or heavy ion irradiation. OER was calculated as the slope of phosphorylated histone H2AX foci/Gy formed at 1 h post irradiation of A549 human non-small cell lung cancer under an oxic condition divided by that under a hypoxic condition. Such OER was about 3 for X-rays and at 13 keV/µm, about 2 at 30 and 50 keV/µm, and about 1 at 65, 80 and 200 keV/µm.
https://www.researchgate.net/publication/319241394_Oxygen_Enhancement_Ratio_in_Radiation-Induced_Initial_DSBs_by_an_Optimized_Flow_Cytometry-based_Gamma-H2AX_Analysis_in_A549_Human_Cancer_Cells
Article Oxygen Enhancement Ratio in Radiation-Induced Initial DSBs b...
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