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Why can healthy cells near an X-ray treatment area often recover better than cancer cells?

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Diagram of the electromagnetic spectrum showing different types of waves arranged by wavelength and frequency, from gamma rays and X-rays to ultraviolet, visible light, infrared, microwave, TV/FM radio, shortwave radio, AM radio, and longwave radio. — X-ray The relationship of X-rays to other electromagnetic radiation within the electromagnetic spectrum.

Healthy cells near an X-ray treatment area often recover better than cancer cells primarily due to differences in their rates of proliferation and their ability to repair genetic damage.

Radiation therapy works by damaging the DNA of cells, which prevents them from replicating or induces apoptosis (programmed cell death). Cancer cells are generally more radiosensitive than healthy cells because they are continuously and rapidly proliferating. Cells are most vulnerable to radiation-induced death when they attempt to divide; because cancer cells divide more frequently than most normal, healthy cells, they are disproportionately affected by the treatment.12

Furthermore, healthy cells that are not actively dividing can often withstand higher doses of radiation without significant injury. When healthy cells do sustain damage, they possess sophisticated DNA repair mechanisms that allow them to fix lesions between radiation fractions. By delivering radiation in smaller, repeated doses—a process known as fractionation—clinicians allow healthy tissues time to repair sublethal damage, thereby minimizing complications while still effectively targeting the more vulnerable, rapidly dividing cancer cells.132