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

Authors


Abstract

Purpose:

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.

Methods:

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.

Results:

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.

Conclusion:

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

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