Neutron Dose Equivalent in Tissue Due to Linacs of Clinical Use

When operating linear accelerators of clinical use at energies above 8 MeV, neutrons are produced when either electron or photon configurations are used [1]. This is mainly due to the interactions of photons and electrons of such energies with the high-Zmaterials present in the accelerator head (target, scattering foils, collimators, etc.) [22]. Because of their high relative biological effectiveness, photoneutrons are a particular source of unwanted out-of-field exposure of patients and several authors have pointed out the possibility of associated risks of secondary cancers after radiotherapy.