A Monte Carlo model of an agility head for a 6 MV Elekta photon beam

Abstract

IntroductionWith the advance in radiotherapy delivery, the need for a method allowing for a precise dose calculation increased. Monte Carlo modelling of radiotherapy dosages has become an important methodology for the evaluation of dose and beam performance, especially given recent advances in radiotherapy. In this study, an Elekta equipped with an Agility multileaf collimator will be modelled and validated in order to be used in further studies. MethodologyA 6 MV photon beam for the Elekta Synergy linear accelerator with an Agility head was simulated, adjusted, and confirmed using the BEAMnrc/EGSnrc algorithm. Tuning involved comparing percentage depth dose with measured data using different incident electron energies, as analyzed using the gamma index. The best energy so calculated was then used with different full half width maximums (FWHMs) and different angular divergences in order to tune the lateral profiles. Output factors for different field sizes were validated with measurements. Then, the validated model was checked for different depths. ResultsFor PDD comparison, the best electron energy was found to be 6.6 MeV, where the gamma analysis is 100%. A 0.15 cm circle FWHM was found to have the best FWHM. with an angular diverge of 0.03°. The output factors match measured values, proving that the model can achieve a suitably high accuracy. ConclusionThe validated model can be used in advanced radiotherapy dose calculation such as in VMAT, IMRT, and Stereotactic radiotherapy. The model needs to be validated in future studies for smaller field sizes, surface dose, and out-of-field dosimetry.