J Liu¹*, S Cozza², J Chang³, J Baker⁴ , (1) Northwell Health, Lake Success, NY, (2) Hofstra University, Hempstead, NY, (3) Northwell Health, Lake Success, NY, (4) Northwell Health, Lake Success, NY

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  J Liu

(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: To provide energy spectra for the Varian TrueBeam linac and have greater understanding of the radiation physics involved.

Methods: We created a TrueBeam Monte Carlo model powered by Geant4 10.3 patch-01, Gate v8.0 and the phase-space files from TrueBeam Monte Carlo Data Package v2 released by Varian. Simulations of 6 and 15 MV beams were performed both in air and in a 60x60x60 cm water phantom at 100 cm source-to-surface distance. Model verification was completed with percent depth dose (PDD) and dose profile simulations. Photon energy spectra in a cylinder with a radius of 1.5 cm and height of 1 cm along the central-axis for various field sizes were collected at the isocenter in air and 1.5, 10 and 20 cm in the water phantom.

Results: Analysis of the PDDs and profiles showed that simulations agreed well with experimental values. The average energies () of the 6 and 15 MV beams for a 10x10 cm field in air is 1.73 MeV and 3.74 MeV, respectively, less than 1/3 of the nominal maximum photon energies for those beams which are commonly assumed. These results are significantly lower than the previously reported values for a Clinac-20, 1.92 and 4.11 MeV, respectively. The of the 6MV beam is close to the reported value (1.71 MeV) for Clinac-2300. The of the 6 MV beam in water at 10 cm depth is 1.38 MeV, 0.11 MeV lower than that reported for the Clinac-2300.

Conclusion: Energy spectra of the 6 and 15 MV beams in air and water from Varian Truebeam linac were simulated. The energy spectrum of Varian Truebeam linac can be very differet from that of other Varian linac machines.

Keywords

Energy Spectrum, Monte Carlo

Taxonomy

TH- External beam- photons: Monte Carlo

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