| This thesis is directed towards dose calculations for clinical electron and photon beams using the Monte Carlo method. Firstly, dose calculations for a range of electron and photon beams from a medical linear accelerator were performed. Electron and photon beams of nominal energy 6–20 MeV and 6–15 MV, field size 1 x 1- to 20 x 20-cm2 and 4 x 4- to 25 x 25-cm2 respectively were simulated for square and rectangular fields. Calculated dose profiles on central and transverse axes of the beams, output factors and heterogeneity correction factors were consistent with measurements of the same in homogeneous and heterogeneous phantoms at the 1–2% level. Secondly restricted mass collision stopping-power ratio variations with field size, beam orientation, phantom composition and detector material were studied for various clinical electron beams. The water-to-air ratios for narrow beams were within 1% of the corresponding ratios for broad beam reference conditions on the central axis. The variations were less for water-to-detector materials such as lithium fluoride and PMMA. Thirdly, dose calculations were performed for intensity modulated photon beams from enhanced dynamic wedges or multileaf collimators in static or step-and-shoot mode. For the enhanced dynamic wedges, 15 and 60 degree wedges were simulated for field sizes that ranged from 4 x 4- to 25 x 25-cm2. A component module was introduced to simulate the shape of the multileaf collimator leaves to account for the screws, tongue-and-groove stepped sides, rounded or divergent leaf ends and interleaf air gaps. Transverse dose profiles were consistent with measurements to within 3% for enhanced dynamic wedges of wedge angle ranging from 15 to 60 degrees and the multileaf-collimated fields studied. |
