[Basic Knowledge of Neutron: Generation of Neutrons Accompanied with Particle Therapy].

Particle therapy uses high-energy charged particles, which cause nuclear reactions with a beam limiting device and a patient, resulting in the generation of high-energy secondary neutrons. These secondary neutrons cause low-dose exposure to organs far from the treatment target, and have a high biological effect due to their energy characteristics, which may cause of secondary cancers after radiotherapy. This article describes the neutron generation mechanism (cross section, and energy spectrum), interaction with the secondary neutron source (beam limiting device, and the patient), measurement of neutrons, and considerations for radiation protection of patients from secondary neutrons, generated by proton and carbon beam radiation therapy.