Radiation therapy uses high-energy radiation to kill cancer cells by damaging their DNA directly or create charged particles (free radicals) within the cells that can in turn damage the DNA. X-rays, gamma rays, and charged particles are types of radiation used for cancer treatment. The radiation used for cancer treatment may come from a machine outside the body (external radiotherapy), or it may come from radioactive material placed in the body near Tumour cells (brachytherapy) or injected into the bloodstream (I131 for thyroid cancers). A patient may receive radiation therapy before, during, or after surgery, depending on the type of cancer being treated. The type of radiation therapy may vary of the size of the Tumour, and location of the Tumour.

Intensity Modulated Radiotherapy uses hundreds of tiny radiation beam-shaping devices, called collimators, to deliver a single dose of radiation and modulating different doses to different areas of the Tumour. Intensity guided Radiotherapy using repeat imaging CT and PET scans to reduce dose to normal tissues and enhance dose to specific areas of Tumour. Stereotactic radiosurgery (SRS) can deliver one or more high doses of radiation to a small Tumour by using accurate image-guided Tumour targeting and patient positioning systems. Therefore, a high dose of radiation can be given without excess damage to normal tissue. Electron beams are also used to irradiate superficial tumors such as on skin while protons beams are shown to have fewer side effects than normal photons in treating deeper tissues. Hyperthermia has also been used in conjunction with radiation to improve the treatment outcomes in several cancers.