Dose-volume Histograms Comparison From Two Different Beam Configurations In The Monte Carlo Simulation of 6MV Clinac2100 Using PRIMO Program

Abstract

The Monte Carlo (MC) method is widely considered to provide the most accurate dose distribution in external beam radiotherapy. A self-contained, full MC linac simulator and dose calculator, PRIMO is a windows-based, freely-distributed software which allows the importation of external compliant phase-space files among its many capabilities. Using PRIMO, a Varian Clinac2100 is simulated at 6 MV nominal energy for 108 number of histories. The dose calculations are compared using two different initial electron beam configurations. The tuned-beam profile has initial electron beam energy of 6.26 MeV, 0.150 MeV full-width-half-maximum (FWHM), 0.150 cm focal spot FWHM and 2 degrees beam divergence. The default configuration given in PRIMO has 5.40 MeV as initial electron beam energy and zero values for all the other beam parameters. A brain computerized tomography (CT) volume is imported into PRIMO and using its contouring tools, these structures are delineated: a hypothetical grosstumor volume (GTV), the brain, the left and right eye lens. The CT volume is irradiated with two parallel-opposed fields of size 10 cm by 10 cm with the brain conformed using the 52-leaf MLC. The dose-volume histogram (DVH) of the GTV and the brain for the tuned-beam profile has a larger extent into the high dose region compared to the DVHs of the default beam configuration. The dose given to 95% of the volume (D95) and the percentage of the volume receiving a dose equal to 95% (V95) are also compared. The GTV for the default beam profile has D95 = 86.31% with V95 = 0.44%, while for the tuned-beam profile, D95 = 88.30% with V95 = 0.95%. For the brain, D95 = 2.55% with V95 = 1.13% for the default profile while the tuned beam profile gives D95 = 2.43% with V95 = 2.33%. For the left [right] lens, D95 = 0.15% [D95 = 0.11%] for the default profile and D95 = 0.16% [D95 = 0.081%] for the tuned-beam profile. Both beam profiles give V95 = 0% for the left- and right- eye lens.