Estimation of neutron production from accelerator head assembly of 15 MV medical LINAC using FLUKA simulations

For the production of a clinical 15 MeV photon beam, the design of accelerator head assembly has been optimized using Monte Carlo based FLUKA code. The accelerator head assembly consists of e–γ target, flattening filter, primary collimator and an adjustable rectangular secondary collimator. The accelerators used for radiation therapy generate continuous energy gamma rays called Bremsstrahlung (BR) by impinging high energy electrons on high Z materials. The electron accelerators operating above 10 MeV can result in the production of neutrons, mainly due to photo nuclear reaction (γ, n) induced by high energy photons in the accelerator head materials. These neutrons contaminate the therapeutic beam and give a non-negligible contribution to patient dose. The gamma dose and neutron dose equivalent at the patient plane (SSD = 100 cm) were obtained at different field sizes of 0 × 0, 10 × 10, 20 × 20, 30 × 30 and 40 × 40 cm2, respectively. The maximum neutron dose equivalent is observed near the central axis of 30 × 30 cm2 field size. This is 0.71% of the central axis photon dose rate of 0.34 Gy/min at 1 μA electron beam current.