Development and commissioning of a Monte Carlo photon beam model for Varian Clinac 2100EX linear accelerator.

Monte Carlo modeling of a linear accelerator is the first and most important step in Monte Carlo dose calculations in radiotherapy. We developed a photon beam model for Varian 2100EX for dose calculation purposes using MCNP4C Monte Carlo code. Results of our modeling were in close agreement with our measurements. The effect of beam width on percentage depth doses and beam profiles was studied. Our results showed that electron beam width could be tuned using large field beam profile at the depth of maximum dose.