Radiation therapy uses high-energy radiation to kill cancer cells by damaging their:

Radiation therapy is specifically designed to target and damage the DNA within cancer cells. The effectiveness of this treatment relies on the high-energy radiation causing breaks in the DNA strands, which disrupts the cell's ability to replicate and function properly. When a cancer cell's DNA is damaged beyond repair, it leads to apoptosis, or programmed cell death, effectively reducing or eliminating the cancer.

While the cell membrane, Golgi body, and mitochondria are essential parts of a cell, the crucial target in radiation therapy is the DNA, as it holds the genetic instructions necessary for cell division and survival. Damage to DNA is the key mechanism by which radiation therapy achieves its anticancer effects, making this the correct answer.