Modification of binomial lateral spreading function for oblique electron beams in pencil beam algorithm based on Monte Carlo simulations

Background: the present study aimed to evaluate the accuracy of the pencil beam algorithm (pba) dose calculations with modified binomial lateral spreading function for oblique electron beams compared with monte carlo simulations (mcs), as a standard method. materials and methods: the oblique pencil beams were simulated using mc code, and lateral dose distributions of oblique (10 and 12 mev) electron beams were calculated in homogeneous water and heterogeneous slab phantoms (different materials of paraffin, carbon, and rw3). the mc dose calculations were used to modify the parameters of the binomial gaussian lateral spreading function of pba. the dose profiles of oblique electron beams were calculated by modified pba and compared with mcs in both phantoms using gamma analysis with a 2% dose difference (dd) and 2 mm distance to agreement (dta) constraints. results: the average difference in dose profiles between pba and mc calculations was 0.88% and 0.76% for water and slab phantoms, respectively. the mean gamma pass rate was 97.4% and 97.8% for water and slab phantoms, respectively. the gamma pass rates were above 95%, except for the dose profile of the water phantom irradiated with 10 mev at a depth of 1 cm. conclusion: the modified pba dose calculation results showed an excellent agreement with mcs in the two phantoms irradiated with oblique 10 mev and 12 mev electron beams. our approach of modifying the pba can be used for other charged particle dosimetry and clinical applications, especially electron and proton dosimetry.