Which cell type is least sensitive to ionizing radiation damage?

• A. Cells that divide quickly
• B. Red blood cells
• C. Cells that divide slowly
• D. Muscle cells

Answer: (C)

Ionizing radiation damages DNA, and a cell’s radiosensitivity tracks how actively it divides and how differentiated it is. According to the relationship between proliferation and sensitivity, cells that divide slowly are less likely to incur lethal consequences from a given dose, because they have fewer mitotic events to interrupt and more time for DNA repair between divisions. In contrast, rapidly dividing cells pass through DNA replication and mitosis frequently, so radiation-induced DNA damage is more likely to be propagated and lethal.

So, when choosing the least sensitive cell type, the one that divides slowly fits best. Rapidly dividing cells are the most vulnerable, while mature or non-dividing cells tend to be more resistant, but the defining factor here is the slow division rate.