Broad and small field commissioning of a 6 MV Elekta synergy using FLUKA and Geant4 Monte Carlo models

This study aims to reproduce therapeutic dose distributions in small-field conditions for an Elekta Synergy system using Monte Carlo (MC) simulations. The Fluka and Geant4 codes were employed to simulate the Linac head. Output factors, percentage depth doses (PDDs), and off-axis dose profiles were computed for field sizes ranging from 2×2 cm2 to 20×20 cm2, including an asymmetric field size of 8×8 cm2 (3 + 5 cm in one axis, 4 + 4 cm in the other), in water with a source surface distance of 90 cm. Analysis of the beam spectrum generated by the linac treatment head demonstrated strong agreement between the beam parameters for both MC codes. The calculated output factors at a depth of 10 cm in water agreed within 1.52% with measured values for both MC codes. Validation of the beam accuracy was conducted by comparing the MC calculated PDDs and dose profiles with measured data via gamma index analysis. Over 95% of the points for all simulations met the stringent acceptability criteria of 2%/2 mm.