Which radiobiologic effect is most frequently observed in growing tissue exposed to ionizing radiation?

• A. Nuclear disintegration
• B. Vacuolization
• C. Cessation of cell division
• D. Altered protoplasmic viscosity

Answer: (C)

Ionizing radiation damages DNA, and tissues that are actively growing have many cells that are ready to divide. The most common radiobiologic response in this situation is a halt in the ability of cells to complete division. Checkpoints detect DNA damage and pause the cell cycle to allow for repair; if damage cannot be repaired, cells may die after attempting to divide. This reduction in cell proliferation is the characteristic effect in growing tissue. Nuclear disintegration, vacuolization, or changes in protoplasmic viscosity can occur with cell injury, but they are not the primary and most frequent outcome in rapidly dividing tissue exposed to radiation.