Particle therapy is a form of external beam radiotherapy using beams of energetic protons,neutrons, or positive ions for cancer treatment. The most common type of particle therapy as of 2012 is proton therapy. Although a photon, used in x-ray or gamma ray therapy, can also be considered a particle, photon therapy is not considered here. Additionally, electron therapy is generally put into its own category. Because of this, particle therapy is sometimes referred to, more correctly, as hadron therapy (that is, therapy with particles that are made of quarks).
Neutron capture therapy might be considered a type of particle therapy, but it is not discussed here, as the damage it does to tumors is mostly from energetic ions produced by the secondary nuclear reaction after the neutrons in the external beam are absorbed into boron-10 (or occasionally some other nuclide), and not due primarily to the neutrons themselves. It is therefore a type of secondary particle therapy.
Muon therapy, a rare type of particle therapy not within the categories above, has occasionally been attempted.
重粒子線がん治療（じゅうりゅうしせんがんちりょう、英語: heavy particle therapy,charged particle radiotherapy, heavy ion therapy, など）とは、線量局在性の高い治療が可能という性質を持つことから、炭素イオン線でがん病巣をピンポイントで狙いうちし、がん病巣にダメージを十分与えながら、正常細胞の有害事象を最小限に抑えることが可能とされる最先端の放射線療法のうちの一つ。