Monte Carlo study of a free flattening filter to increase surface dose on 12 MV photon beam

Several investigations reported the dosimetric properties offlattening filter free photon beams to enhance the entrance dose in thesurface and build up region. this paper was aimed to investigate the effect ofthe flattening filter free to enhance the dose at the surface and buildupregion. materials and methods: a 12 mv photon beam of a linear acceleratorwas modeled and developed in both flattening filter and flattening filter freemodes using the monte carlo beamnrc code. for both modes, the beamdosimetric features, including central axis absorbed doses and photon energyspectra were investigated. results: a remarkable increase in the dose rate onthe surface and build up region were attained with the flattening filter freemode. at the depth of 0 mm on 2×2 cm2, 4×4 cm2, 5 × 5 cm2, and 10×10 cm2field sizes, the surface doses between flattening filter mode and flatteningfilter free mode were augmented from 27.33% to 33.78%, from 28.89% to35.75%, from 29.44% to 36.39%, and finally from 35.10% to 47.46%,respectively. at the depth of 25 mm for field size from 2×2 cm2 to 10×10 cm2,the buildup doses for flattening filter mode and flattening filter free modewere augmented from 124.89% to 136.72% and from 132.21% to 142.67%,respectively. conclusion: a significant increase in the entrance and buildupdose rate was observed when using an unflattened photon beam, which canbe a benefit for the treatment of some skin cancers.