Biologic material irradiated under hypoxic conditions is less sensitive than when irradiated under oxygenated conditions. Which option correctly states this?

Biologic material irradiated under hypoxic conditions is less sensitive than when irradiated under oxygenated conditions. Which option correctly states this?

• A. A more sensitive than oxygenated
• B. B less sensitive than anoxic
• C. C less sensitive than oxygenated
• D. D unaffected by the presence or absence of oxygen

Answer: (C)

Oxygen increases the damage that radiation can cause to cells because it helps fix the free-radical injuries created by irradiation, making the damage permanent and more lethal. When biological material is hypoxic, there is less oxygen available to fix that damage, so more of the initial damage can be repaired and the overall effect is reduced. That means irradiating under hypoxic conditions is less sensitive than irradiating under oxygenated conditions. This relationship is often summarized by the oxygen enhancement ratio, which for many low LET radiations is about 2–3, indicating you need a higher dose to achieve the same effect in hypoxic cells. So the statement reflecting that hypoxic irradiation is less sensitive than oxygenated irradiation is the correct one. The idea that oxygen has no effect, or that hypoxia would be more sensitive, contradicts the well-established oxygen effect.

Oxygen increases the damage that radiation can cause to cells because it helps fix the free-radical injuries created by irradiation, making the damage permanent and more lethal. When biological material is hypoxic, there is less oxygen available to fix that damage, so more of the initial damage can be repaired and the overall effect is reduced. That means irradiating under hypoxic conditions is less sensitive than irradiating under oxygenated conditions. This relationship is often summarized by the oxygen enhancement ratio, which for many low LET radiations is about 2–3, indicating you need a higher dose to achieve the same effect in hypoxic cells. So the statement reflecting that hypoxic irradiation is less sensitive than oxygenated irradiation is the correct one. The idea that oxygen has no effect, or that hypoxia would be more sensitive, contradicts the well-established oxygen effect.