Radiation therapy is a common form of cancer treatment that uses high-energy radiation to shrink tumors and kill cancer cells. It works by damaging the DNA inside cancer cells, which prevents them from growing and spreading. Radiation therapy can be delivered externally using machines that target the tumor from outside the body, or internally through implants or injections. It is often used in combination with surgery and/or chemotherapy to provide the most effective treatment for cancer patients. Radiation therapy can also be used to alleviate symptoms and improve quality of life for patients with advanced-stage cancer.