Pencil-Beam Fluence Evaluation Based on Monte Carlo Simulations Algorithm of High Energetic Treatment Photons

BACKGROUND: The accurate calculation of doses during external radiotherapy sessions is necessary. Recently, the models used for this purpose have been the point kernel, pencil-beam, and collapsed cone superposition/convolution combination models. METHODS: In this study, it is aimed to determine point/pencil-beam kernels to be used in dose calculations. For this purpose, tallying pencil-beam fluence based on Monte Carlo (MC) simulations is investigated by scoring a volume of interest centered in a cubic water phantom at a depth of 10 cm and the irradiated field of 10 cm × 10 cm. The fluence is calculated for each mono-energetic photon ranging from 0.25–6 MV at increments of 250 keV. RESULTS: The output of the four fluence kernels along the depth Z around the central axis is categorized for both the primary and secondary photons and electrons. Here, a database for pencil-beam kernels is established for each category. For validation purposes, other MC simulations are carried out for fluence calculations as produced by the predetermined poly-energetic spectra for a Varian 6 MV linear accelerator. CONCLUSIONS: The net results show a good fit of the two convoluted fluence spectra quantities for both mono-energetic and poly-energetics-based simulations except little singular peaks.