ABSTRACT
Radiological considerations for proton accelerators have played an important role, since the construction and operation of particle accelerators first occurred in the 1930s. Proton therapy accelerators operate in the intermediate energy range. The interaction of protons with any material in their path results in the production of secondary radiation. Losses of the primary proton beam may occur along the beamline or in beamline components. Beam losses occur in the synchrotron and cyclotron during injection, during energy degradation in the cyclotron, during beam transport to the treatment room, in passive scattering systems, range degraders, and modulators, and in beam-shaping devices such as collimators, apertures, and range compensators placed near the patient. The residual nucleus evaporates particles such as alpha particles and other nucleons, which contribute only to local energy absorption. A large fraction of the energy in the cascade is transferred to a single nucleon.
