Monte Carlo Simulations ofChemical Vapour DepositionDiamond Detectors

摘要

Chemical Vapour Deposition (CVD) diamond detectors were modelled for dosimetryof radiotherapy beams. This was achieved by employing the EGSnrc Monte Carlo(MC) method to investigate certain properties of the detector, such as size, shapeand electrode materials. Simulations were carried out for a broad 6 MV photonbeam, and water phantoms with both uniform and non-uniform voxel dimensions. Anumber of critical MC parameters were investigated for the development of a modelthat can simulate very small voxels. For a given number of histories (100 million),combinations of the following parameters were analyzed: cross section data,boundary crossing algorithm and the HOWFARLESS option, with the rest of thetransport parameters being kept at default values. The MC model obtained with theoptimized parameters was successfully validated against published data for a 1.25MeV photon beam and CVD diamond detector with silver/carbon/silver structure withthicknesses of 0.07/0.2/0.07 cm for the electrode/detector/electrode, respectively.The interface phenomena were investigated for a 6 MV beam by simulating differentelectrode materials: aluminium, silver, copper and gold for perpendicular andparallel detector orientation with regards to the beam. The smallest interfacephenomena were observed for parallel detector orientation with electrodes made ofthe lowest atomic number material, which was aluminium. The simulatedpercentage depth dose and beam profiles were compared with experimental data.The best agreement between simulation and measurement was achieved for thedetector in parallel orientation and aluminium electrodes, with differences ofapproximately 1%.In summary, investigations related to the CVD diamond detector modelling revealedthat the EGSnrc MC code is suitable for simulation of small size detectors. Thesimulation results are in good agreement with experimental data and the model cannow be used to assist with the design and construction of prototype diamonddetectors for clinical dosimetry. Future work will include investigating the detectorresponse for different energies, small field sizes, different orientations other thanperpendicular and parallel to the beam, and the influence of each electrode on theabsorbed dose.