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A Monte Carlo Dose Calculation Framework for Electron Beams On Varian TrueBeam

A Rodrigues

A Rodrigues1,2*, D Sawkey3 , F Yin1,2 , Q Wu1,2 , (1) Duke University Medical Center, Durham, NC, (2) Medical Physics Graduate Program, Duke University Medical Center, Durham, NC, (3) Varian Medical Systems, Palo Alto, CA


SU-E-T-386 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: The design of the linac head is different for TrueBeam than Clinac, and there are differences in measured dose distributions in water phantoms between TrueBeam and Clinac for electron beams. Therefore, MC models for Clinac may not be applied directly to the Truebeam linac. The purpose of this study is to validate a Monte Carlo (MC) dose calculation framework for electron beams on Varian TrueBeam with phase space files provided by Varian.

Methods: The particle histories from the phase space file were used as input for the down-stream simulation including jaws, applicators, and water phantom. MC packages BEAMnrc/DOSYXZnrc were used. The down-stream beam components were modeled according to manufacturer specifications and the dose distributions were compared with the measured data of standard cones. The measurements were performed in a water phantom with a p-type electron field diode (diameter 0.2cm) and ion chamber (CC13). Depth dose and orthogonal profiles at depths defined by R₁₀₀, R₅₀, Rp were compared.

Results: Preliminary results for a 16 MeV phase space and 10x10, 15x15, and 20x20 cm² applicator are presented. Simulations were run for a statistical uncertainty of <2% at depth of maximum dose for a voxel resolution of 0.5x0.5x0.2cm². Dose and range differences for the PDD profiles were within 2% and 1 mm, respectively. Dose differences within the central 80% of the beam width for the orthogonal profiles at depth of maximum dose were less than 2% for the 10x10, 15x15, and 20x20 cm² applicator, respectively.

Conclusion: Varian electron phase space files simulations are in agreement with measured commissioning data. These phase space files can be used in the simulation of TrueBeam linacs, and will provide reproducibility across publications. Analyses for all electron energies and standard applicators are under way and results will be included in the presentation.

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