Radiation therapy is a form of cancer treatment where cancer cells are destroyed using high-energy X-rays or particles such as protons. It is a painless and non-invasive local treatment that damages the DNA of the cancer cells and leads to the death of the cancer cells in the area irradiated. It is usually given from a machine outside the body (called external-beam radiation therapy). It is one among the pillars of cancer treatment (others being surgery, chemotherapy, precision oncology, immunotherapy) which has been used for more than a century.