What effect does radiation therapy have on cancer cells?

Radiation therapy primarily functions by damaging the DNA within cancer cells. This is achieved through the production of free radicals and ionization of the DNA structure, causing breaks in the DNA strands. When the DNA is damaged beyond a certain point, it cannot be effectively repaired, leading to cell cycle arrest and, ultimately, programmed cell death (apoptosis).

The goal of radiation therapy is to selectively target cancer cells while minimizing damage to surrounding normal tissues. However, the sensitive nature of cancer cells to radiation, coupled with their typically high rates of division, makes them more susceptible to DNA damage compared to normal cells. Therefore, this mechanism of inducing DNA damage and ensuing cell death is why option C is the correct choice in the context of how radiation therapy affects cancer cells.