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

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.

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.

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.

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.