External-Beam Radiotherapy

External-beam radiotherapy usually uses an electrical device called a linear accelerator, where radiation is directed at the patient with no direct contact between the radiation source and the patient. It is the most common form. Types of external-beam radiotherapy: photon therapy and particle therapy. There are two types of external-beam radiotherapy. The most well-known and widely used is photon therapy; because it is so widely used, it is highly reliable with known, predictable results. Its drawback is that the intermediate and low doses around the tumor are higher than with particle therapy, which may cause more side effects in some cases. The other type is particle therapy, which also has two kinds: electrons, which are small and cannot reach a deep target inside the body (used, for example, for some skin cancers or superficial tumors), and proton therapy, which can reach deep tumors, with intermediate and low doses around the tumor that are lower than with photons.