How does the presence of oxygen affect cell/tissue radiosensitivity?

• A. It decreases radiosensitivity
• B. It has no effect
• C. It increases radiosensitivity
• D. It makes radiosensitivity variable

Answer: (C)

The presence of oxygen increases radiosensitivity in cells and tissues due to a phenomenon known as the oxygen effect. Oxygen enhances the effectiveness of radiation therapy because it stabilizes free radicals generated by ionizing radiation. In anoxic (low or no oxygen) conditions, these free radicals, which are crucial for damaging the molecular structures of DNA, may recombine or be repaired, thereby reducing the overall damage from radiation exposure.

When oxygen is present, it reacts with the free radicals to form more stable molecules that cause significant damage to the DNA. This increased likelihood of DNA damage leads to a higher probability of cell death, making tumors more sensitive to radiation therapy when they are well-oxygenated. Consequently, targeting tumors in oxygen-rich environments can lead to improved treatment outcomes in radiotherapy, underscoring the critical role of oxygen in influencing radiosensitivity.