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Benchmarking of Monte Carlo simulation of bremsstrahlung from thick targets at radiotherapy energies
Author(s) -
Faddegon Bruce A.,
Asai Makoto,
Perl Joseph,
Ross Carl,
Sempau Josep,
Tinslay Jane,
Salvat Francesc
Publication year - 2008
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2975150
Subject(s) - bremsstrahlung , monte carlo method , photon , physics , fluence , photon energy , spectral line , beam (structure) , electron , computational physics , monte carlo method for photon transport , atomic physics , yield (engineering) , nuclear physics , optics , dynamic monte carlo method , irradiation , statistics , astronomy , mathematics , direct simulation monte carlo , thermodynamics
Several Monte Carlo systems were benchmarked against published measurements of bremsstrahlung yield from thick targets for 10 – 30 MV beams. The quantity measured was photon fluence at 1 m per unit energy per incident electron (spectra), and total photon fluence, integrated over energy, per incident electron (photon yield). Results were reported at 10 – 30 MV on the beam axis for Al and Pb targets and at 15 MV at angles out to 90° for Be, Al, and Pb targets. Beam energy was revised with improved accuracy of 0.5% using an improved energy calibration of the accelerator. Recently released versions of the Monte Carlo systems EGSNRC , GEANT4 , and PENELOPE were benchmarked against the published measurements using the revised beam energies. Monte Carlo simulation was capable of calculation of photon yield in the experimental geometry to 5% out to 30°, 10% at wider angles, and photon spectra to 10% at intermediate photon energies, 15% at lower energies. Accuracy of measured photon yield from 0 to 30° was 5%, 1s . d . , increasing to 7% for the larger angles. EGSNRC and PENELOPE results were within 2s . d .of the measured photon yield at all beam energies and angles, GEANT4 within 3s . d .Photon yield at nonzero angles for angles covering conventional field sizes used in radiotherapy (out to 10°), measured with an accuracy of 3%, was calculated within 1s . d .of measurement for EGSNRC , 2s . d .for PENELOPE and GEANT4 . Calculated spectra closely matched measurement at photon energies over 5 MeV . Photon spectra near 5 MeV were underestimated by as much as 10% by all three codes. The photon spectra below 2 – 3 MeV for the Be and Al targets and small angles were overestimated by up to 15% when using EGSNRC and PENELOPE , 20% with GEANT4 . EGSNRC results with the NIST option for the bremsstrahlung cross section were preferred over the alternative cross section available in EGSNRC and over EGS4 . GEANT4 results calculated with the “low energy” physics list were more accurate than those calculated with the “standard” physics list.