The Role of Oxygen in Radiation Effects

1. Oxygen and Radiation-Induced Damage

The presence or absence of oxygen can significantly affect the extent of radiation-induced damage in biological tissues. Free radicals produced during radiation interactions are highly reactive and can interact with nearby molecules, potentially leading to DNA damage. Oxygen, due to its unique chemical properties, can enhance this damage.

2. How Oxygen Enhances Radiation Damage

When radiation generates free radicals, molecular oxygen (O₂) can react with these radicals, leading to the formation of highly toxic molecules that further damage cellular structures. Oxygen’s unpaired electrons make it readily reactive, and the following reactions illustrate how oxygen can amplify biological damage:

• Oxygen's Role: Oxygen increases the reactivity of free radicals, making DNA and other cellular molecules more susceptible to damage.
• Effects: The resulting molecules, like hydrogen peroxide (H₂O₂) and reactive oxygen species (ROS), are highly toxic and can lead to cell death or mutations.

3. Oxygen Enhancement Ratio (OER)

The oxygen enhancement ratio (OER) quantifies the effect of oxygen on radiation damage. It is defined as the ratio of the dose required to achieve the same biological effect in an anoxic (no oxygen) environment to the dose required in an oxygenated environment. The OER is higher for low LET radiation and lower for high LET radiation.

• Low LET Radiation (e.g., γ-rays): The OER is approximately 3, meaning that the presence of oxygen makes the tissue about three times more sensitive to radiation.
• High LET Radiation (e.g., α-particles): The OER approaches 1.0, indicating that oxygen has little to no effect on enhancing radiation damage for high LET radiation.