How does the presence of oxygen affect the radiosensitivity of cells?

The presence of oxygen significantly increases the radiosensitivity of cells, which is a key concept in radiobiology. This phenomenon is often referred to as the "oxygen enhancement ratio." When cells are exposed to ionizing radiation in the presence of oxygen, the radiation is more effective in causing damage to the DNA and other critical cellular structures.

Oxygen enhances the formation of free radicals when radiation interacts with water molecules in cells. These free radicals are highly reactive and can cause extensive cellular damage, particularly to DNA. In conditions where oxygen levels are low, such as in hypoxic tumors, the effectiveness of radiation therapy is reduced because the formation of these damaging free radicals is diminished.

Therefore, the presence of oxygen plays a crucial role in enhancing the effects of radiation on cells, making them more susceptible to damage. This understanding is vital for designing effective radiation therapy treatments, as it highlights the importance of oxygen levels in the tumor microenvironment.