SU-E-T-697: Simple and Efficient Modeling of the Varian TrueBeam Linac Using the GATE Monte Carlo Platform




To investigate the use of the relatively new Geant4 Application for Tomographic Emission (GATE) Monte Carlo (MC) platform for radiotherapy applications, by developing a model of the Varian TrueBeam™ linac.


Multiple 6 MV phase space files were provided by Varian, serving as a simulation particle source. Modeling of the jaws and multileaf collimator (MLC) in GATE's macro structured environment was automated through the use of an in-house developed Python program. Profiles and percentage depth doses (PDD) were compared between MC calculations, diode, ion chamber and radiochromic film measurements for six square fields ranging in size from 1 × 1 cm2 to 40 × 40 cm2 at five different depths. The MLC model was evaluated through comparison to radiochromic film for an “E” shaped field defined by the MLCs at two different depths.


Profiles and PDDs of MC calculated values for each field size and depth were evaluated against measurements using a tight 3%/1 mm gamma criteria. It was found that 28 out of 30 square field profiles have a gamma pass rate of ≥90%, 20 of which achieved at least a 95% pass rate. All PDDs were found to have at least a 97% pass rate. When compared to film measurements, 97% and 99% of points met the gamma criteria for the MLC shaped field along the inline and crossline axes respectively, while 100% of points achieved the criteria along both axes at a depth of 50 mm.


GATE provides a valid, efficient and simple to use MC platform to model medical linear accelerators for the purpose of radiotherapy dose calculation.