Radiation therapy is performed in two ways: internal radiation therapy and external radiation therapy. In internal radiation therapy, the source of the radiation (radioactive material) is placed in the patient’s body (inside or near the tumor / cancerous tissue) and the tumor / cancerous tissue is destroyed by the dose of the radioactive material decay. In external radiation, the source of radiation is outside the patient’s body, and the patient is exposed to radiation during treatment sessions. Various radiations are used in external radiation therapy, including; gamma rays and photons (X-rays), electrons, protons and ions (for example, carbon ions). Gamma rays are obtained from radioactive sources (usually cobalt-60), but other beams are generated by accelerators.

Electrons have a low penetration depth and are not used to treat tumors / cancerous tissues inside body. In recent years, radiation therapy with gamma beams have been used far less frequently, and gamma-beam radiotherapy centers have become scarce. In recent years, for some types of cancer, radiation therapy using protons and ions (currently only carbon ions) is preferable to photons (also known as conventional radiation therapy).