How does oxygen affect tissue radiosensitivity?

Tissue radiosensitivity is significantly influenced by the presence of oxygen, a phenomenon known as the oxygen effect. When tissues are oxygenated, they exhibit increased sensitivity to radiation. This is primarily due to the fact that oxygen enhances the formation of free radicals when radiation interacts with biological tissues. These free radicals can cause greater cellular damage and increase the likelihood of irreparable DNA strand breaks, ultimately leading to cell death.

In an oxygen-rich environment, the radiation-induced damage does not undergo efficient repair, compared to an anoxic (low-oxygen) environment where the cells can repair some of the damage that occurs. Thus, when tissues are well-oxygenated, the likelihood of severe damage and loss of cellular integrity increases, making them more vulnerable to the effects of radiation exposure. This understanding is essential in the context of radiotherapy, where the timing and delivery of oxygen can play a critical role in treatment effectiveness.