The use of high-energy ionizing radiation (such as X-rays, gamma rays, or charged particles) to locally destroy cancer cells. The radiation damages the DNA within the target cells, leading to cell death, primarily during mitosis. Modern techniques like IMRT and SBRT allow for highly precise targeting of tumors, maximizing the dose to the cancer while minimizing exposure to surrounding healthy tissues. It can be used as a primary treatment, adjuvantly, or for palliation of pain or bleeding.