Abstract
Medical linear accelerators (linacs) are used extensively in modem radiotherapy for their flexibility and versatility. As the treatment regime moves from low-energy photon beams to high-energy beams, photoneutrons produced in the linac head components become important. This work used the general purpose Monte Carlo code MCNPX to model the Varian Clinac, 2100C linac with a 15 MV photon beam. Simulations are carried out for several field sizes commonly encountered in radiotherapy. Photoneutron productions in various head components are estimated from the photon fluence and the photoneutron production cross sections. The results serve as a basis for further studies on using the linac as an alternative neutron source in BNCT and radiation protection issues arising from photoneutrons in the treatment room.