The oxygen enhancement ratio (OER) for low LET radiation such as x-rays in mammalian cells is approximately 2.5 to 3. Clinically, this means:

• A Oxygenated cells need about three times more dose than hypoxic cells for the same level of killing
• B Hyperbaric oxygen reduces tumour control probability
• C Oxygen protects normal tissues from radiation injury
• D Hypoxic tumour cells need about two and a half to three times more dose than well-oxygenated cells for the same killing ✓

Explanation

Oxygen fixes radiation-induced DNA radical damage, so well-oxygenated cells are killed efficiently while hypoxic cells are relatively radioresistant. An OER of about 3 means roughly three times the dose is needed for the same survival in hypoxic conditions. This is the radiobiological basis for fractionation benefits, since reoxygenation between fractions makes chronically hypoxic tumour cells progressively more sensitive in later fractions.

Reference: Hall and Giaccia, Radiobiology for the Radiologist, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.