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How does brachytherapy deliver radiation directly into a tumor?

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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.

Brachytherapy, also known as internal radiation therapy, delivers radiation directly into a tumor or the surrounding tissue by using specialized delivery devices.12

To administer the treatment, encapsulated radioactive sources—such as isotopes of iridium, cesium, gold, or iodine—are placed into the target area using catheters or needles. These devices, which may take the form of tubes, grains, or wires, are inserted directly into the affected tissue or into a body cavity housing the tumor. In some cases, such as remote brachytherapy, the radioactive source is delivered through tubes to the tumor site and subsequently withdrawn.12

This technique is highly valued in medicine because it allows for the delivery of a high dose of radiation directly to the tumor or tumor bed, which effectively destroys cancer cells while sparing the surrounding healthy tissue from unnecessary exposure.12