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Why are cancer cells often more sensitive to radiation than healthy cells?

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linear accelerator; external beam radiation therapy — radiation therapy External beam radiation therapy (also known as external beam teletherapy, or long-distance therapy) being delivered using a machine known as a linear accelerator.

Cancer cells are often more sensitive to radiation than healthy cells primarily because they are continuously proliferating. Radiation therapy works by causing damage to the DNA within a cell's [nucleus]. While all cells can sustain such damage, cells are most vulnerable to radiation injury when they attempt to divide.1234

Because cancer cells reproduce rapidly and frequently, they are less able to recover from the genetic damage induced by radiation compared to normal, healthy cells that are not always dividing. When radiation causes significant damage to a cell's chromosomes or genes, the cell may be unable to replicate, leading to its death or the induction of apoptosis.31

In contrast, many healthy, nondividing cells—such as those in nerve or muscle tissue—are significantly more resistant to radiation and can withstand higher doses without suffering overt injury. The goal of radiation therapy is to exploit this difference in radiosensitivity to destroy malignant cells while sparing as much surrounding healthy tissue as possible.341