SU-E-T-91: Validation of Geant4 Physics for Ionization Chamber Calculations in Radiotherapy Photon Beams

Medical Physics
M H Chequers, G O Sawakuchi

Abstract

To determine the accuracy of the GEANT4 Monte Carlo toolkit for ionization chamber calculations in radiotherapy photon beams. First, we used the Fano cavity example included in the GEANT4 distribution to validate calculations under Fano conditions. We determined a combination of parameters and physics list that provided results consistent within +/- 0.5% with the Fano theorem. Next we performed simulations to investigate the accuracy of using GEANT4 for ionization chamber calculations. Eight ionization chambers were modeled using detailed manufacturer specifications including A1, A1SL, NE2571, PTW30010, PTW30012, PTW31010, PTW31014 and PTW31016. The absorbed dose to water for a cylindrical water cavity and the absorbed dose to air in the ionization chambers' cavities were scored for 1.25 MeV photons. The ratio of these quantities was then compared to values from EGSnrc simulations. Simulations using the Fano cavity example yielded results within +/- 0.5% with the Fano theorem across 1.25, 3 and 4 MeV incident photon energies. The most accurate and consistent results were obtained using the G4eIonisation ionization model and G4GoudsmitSaundersonMscModel multiple scattering (MS) model with a maximum step size limitation of 0.001 ...Continue Reading

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