charged-particle radiation therapy
Charged particles (such as protons and carbon) can be used to deliver therapeutic radiation. A proton is the charged nucleus of a hydrogen atom (hydrogen atom minus an electron). Standard radiation is delivered with a linear accelerator (LINAC) that delivers photon therapy (akin to high energy light), while protons and other charged particles are generated from a cyclotron. The difference between charged-particle and photon irradiation is that charged particles stop abruptly in the tissue (Bragg peak), so there is less exit dose through normal tissue. A disadvantage of charged-particle therapy is the greater neutron exposure compared with essentially none using photons, and thus the benefit of protons in reducing radiation-associated malignancies is not known and controversial. Proton therapy can be used to deliver intensity-modulated radiation therapy, stereotactic radiation therapy, or stereotactic radiosurgery.