MONTE-CARLO CALCULATIONS OF ELECTRON-BEAM PARAMETERS FOR 3 PHILIPS LINEAR ACCELERATORS

Electron beams from three linear accelerators manufactured by Philips (SL75-20, SL75-14/N and SL15) have been simulated using the EGS4 Monte Carlo code. The linear accelerators demonstrate the change in design from the SL75 range to the SL range. The agreement between experimental and calculated central-axis depth-dose curves is good for all three machines. The calculated energy spectra are shown to be very sensitive to the design of the collimating system. Actual beam energies and those calculated from several range-energy formulae are compared and are closer for the more modern machines. Various levels of sophistication in the models for calculating the central-axis depth-dose curve in the phantom were tested for the SL15 12 MeV beam. The most accurate, which simulates the divergence of the major component of the beam and allows for some correlation between energy and angle, agreed with experiment significantly better than simpler models.