Background: Today, cancer treatment is one of challenges in health and treatment system of any country. With quick development of radiation therapy and chemotherapy in recent years, this question is brought up that which method is more perfect to treat cancer. Methods: Radiation therapy is consisted of several methods including external radiation therapy (e.g. CyberKnife, IMRT, IGRT, SBRT, BNCT, Vero, IORT, Gamma knife, Tomotherapy and Volumetric modulated arc therapy (VMAT)) and internal radiation therapy (e.g. brachytherapy, endoradiotherapy (target radionuclide therapy): radioimmunotherapy and peptide receptor radionuclide therapy) that any one has a special function in cancerous cells destroy. Results: Chemotherapy has still its place in cancer treatment and is used as a current and worldwide method. Nowadays, radiation therapy evolves with a surprising growth. By abandoning Cobalt-60, linear and circular accelerators which are able to accelerate particles, could be used for cancer treatment. CyberKnife, IMRT, IGRT, SBRT, VMAT, tomotherapy and Vero are the most advanced methods used to radiation therapy in all angles which had minimum mistake in radiation to the near intact tissues. Today, brachytherapy by increasing production of treatment radioisotopes by cyclotron and reactor is used in the world. Endoradiotherapy (Target radionuclide therapy): Radioimmunotherapy and peptidereceptor radionuclide therapy are two considerable methods in cancer treatment. Conclusion: In this review, we consider principals and application of radiation therapy in the early 21st century.