When oxygenation of a cell decreases, the sensitivity to densely ionizing radiation will:

• A. increase
• B. decrease
• C. remain the same
• D. vary with dose

Answer: (C)

Densely ionizing, high-LET radiation causes most damage through direct ionization along its track, so the role of oxygen in forming free radicals is much less influential. In this scenario, changing the cell’s oxygen level doesn’t appreciably alter the likelihood of lethal damage, because the damage already occurs directly and is not substantially amplified by oxygen-dependent radical chemistry. That’s why sensitivity stays essentially the same regardless of oxygenation.

The other options imply a notable oxygen-related change (more sensitive with oxygen, less sensitive without, or a dose-dependent variation with oxygen), which isn’t characteristic of high-LET radiation where oxygen has a minimal effect on its biological impact.