How does the presence of oxygen affect radiosensitivity?

How does the presence of oxygen affect radiosensitivity?

• A. Oxygen decreases radiosensitivity
• B. Oxygen has no effect
• C. Oxygen increases radiosensitivity
• D. Oxygen leads to immediate effects

Answer: (C)

The presence of oxygen increases radiosensitivity due to a phenomenon known as oxygen enhancement ratio (OER). When oxygen is present during radiation exposure, it enhances the damaging effects of radiation on cells. This is primarily because oxygen can react with the free radicals formed by ionizing radiation, leading to the production of additional free radicals that cause more extensive damage to cellular structures, including DNA.

In hypoxic (low-oxygen) conditions, cells are less sensitive to radiation because the lack of oxygen limits the effectiveness of the radiation in causing damage. Therefore, oxygen acts as a critical factor in making cells more vulnerable to the harmful effects of ionizing radiation, resulting in increased radiosensitivity. This principle is particularly important in radiotherapy for cancer treatment, as tumors that are more oxygenated tend to respond better to radiation therapy than those that are not.