Cancer treatments that use ionizing radiation, particle beams or radioactive isotopes to damage or destroy tumor cells, delivered externally, internally or intraoperatively. This includes radiotherapy broadly and its core delivery techniques (external beam radiotherapy, intensity-modulated radiotherapy, image-guided radiation therapy, stereotactic body radiotherapy, stereotactic radiation therapy, stereotactic radiosurgery, tomotherapy, hypofractionated high-dose intensity-modulated radiotherapy, FLASH radiotherapy, total body irradiation, whole brain radiotherapy, prophylactic cranial irradiation, intraoperative radiation therapy, intraoperative electron radiation therapy, targeted intraoperative radiotherapy and the isocentric technique used to aim it), radiosurgery platforms (CyberKnife, Gamma Knife radiosurgery), particle and neutron-based modalities (particle therapy, proton therapy, proton beam therapy, fast neutron therapy, boron neutron capture therapy and its therapeutics variant, grenz rays), and radioactive-isotope or radiopharmaceutical treatments (brachytherapy, prostate brachytherapy, radioactive iodine therapy, selective internal radiation therapy, peptide receptor radionuclide therapy, targeted alpha-particle therapy, radioimmunotherapy). A treatment whose primary destructive mechanism is heat, ultrasound, an electric field, a surgical instrument or a drug rather than radiation is grouped elsewhere even when radiation is used alongside it.