Radiation transport calculations for beam therapy with Geant4 toolkit

High energy photon therapy beam from the 50 MV racetrack microtron has been evaluated using the Monte Carlo code Geant4. The spatial and energy distribution of photons, radial and depth dose distributions in a water phantom are calculated for both stationary and scanned photon beams from two different targets, one thin and one thick. Validation of Geant4 electromagnetic physics processes has been done using experimental data of radial dose profiles in a water phantom. Both Geant4 electromagnetic packages standard and low energy were used. The toolkit presented is promising for further development of narrow photon beam therapy.