Monte Carlo characterization of photoneutrons in the radiation therapy with high energy photons: a Comparison between simplified and full Monte Carlo models

The characteristics of secondary neutrons in a high energy radiation therapy room were studied using the MCNPX Monte Carlo (MC) code. Two MC models including a model with full description of head components and a simplified model used in previous studies were implemented for MC simulations. Results showed 4-53% difference between full and with the simplified model in the neutron fluence calculation. Additionally, in full MC model, increase in the field size decreased the neutron fluence but for simplified model, increase in the field size led to increase in neutron fluence. In calculating the neutron and capture gamma ray dose equivalent, simplified model overestimated (9-47%) and (20-61%) respectively in comparison to the full simulated model. However, a close agreement was seen between two models, for field size of 10×10 cm2. for MC modeling of photoneutrons and capture gamma in radiotherapy rooms, the detailed modeling of linac head instead of simplified model is recommended. Iran. J. Radiat. Res., 2010; 8 (3): 187-193 Keywords: Photoneutron, capture gamma rays, Monte Carlo simulation, Linac head modeling