Why is radiation therapy considered a local treatment?

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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.

Radiation therapy is considered a local, or targeted, treatment because its effects are confined to the specific area of the body exposed to the radiation beams.3

Unlike systemic treatments that circulate throughout the entire body, radiation therapy utilizes ionizing radiation—such as X-rays, gamma rays, or particle beams—to destroy cancer cells by damaging their DNA within a defined treatment field. Because the therapy is directed at a specific site, the associated side effects are generally limited to the tissues directly within the path of the radiation beams.123