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How does external radiation therapy differ from brachytherapy?

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Precancerous growth in a human colon — cancer View through an endoscope of a polyp, a benign precancerous growth projecting from the inner lining of the colon.

Radiation therapy is a primary treatment for cancer that utilizes ionizing radiation to destroy malignant cells. The two main techniques for delivering this treatment are external radiation therapy (teletherapy) and brachytherapy (internal radiation therapy).1

External Radiation Therapy (Teletherapy)

External beam therapy uses a device, such as a linear accelerator, to deliver high-energy radiation beams from a distance. This method allows for the precise shaping of the radiation field to target deep-seated tumors while minimizing exposure to surrounding healthy tissue. Treatment is typically administered in repeated small doses, known as fractions, to maximize effectiveness and reduce complications.21

Brachytherapy

In contrast, brachytherapy involves placing radioactive sources—such as isotopes of iridium or cesium—directly into the tumor or a nearby body cavity. By delivering radiation from within, this technique provides a high dose to the target tissue while sparing adjacent healthy structures. Because the source is localized, secondary side effects are often less significant compared to those associated with external beam therapy.31

Would you like to know more about the specific types of cancers treated with these methods?