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Poster — Wed Eve—28: Monte Carlo Study of the Influence of a Novel Transmission Detector on 6 MV Photon Beam
Author(s) -
Asuni G,
McCurdy B,
Jensen M
Publication year - 2009
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3244132
Subject(s) - monte carlo method , electron , fluence , detector , dosimetry , physics , photon , tray , absorbed dose , linear particle accelerator , optics , beam (structure) , cathode ray , materials science , computational physics , radiation , irradiation , nuclear physics , nuclear medicine , mathematics , medicine , mechanical engineering , statistics , engineering
The Monte Carlo technique is used to investigate the influence of a novel transmission detector (IBA Dosimetry, Germany) on a 6MV photon beam. The transmission detector may be used as an in vivo IMRT quality assurance tool, and therefore will be a source of contaminant electrons. This could potentially affect prescribed dose to patients. The linear accelerator together with the transmission detector and a plastic block tray for comparison, were modeled using BEAMnrc/EGSnrc. Electron fluence at different SSDs (70, 80, 90, 100 cm), electron energy spectra, electron angular distributions, and surface doses were calculated. Calculated data were validated against measurements using a fixed parallel plate chamber. Calculated surface dose for both open field and non‐open fields (i.e. TRD and block tray) agree within 3% of measurement. The fluence of contaminant electrons produced in the TRD and block tray fields increases at shorter SSD, but most electrons at shorter SSD are low energy electrons with large angular spread. These electrons contribute less to surface dose at larger SSD because they are either out‐scattered or absorbed in air. Surface doses at different SSDs for the block tray are higher than those of the TRD. Contribution of contaminant electrons to dose in the buildup region increases with increasing field size. For a 20 × 20cm 2field, the contribution of electrons is 9.8 % and 8.6% for block tray and TRD respectively, while for a smaller 3 × 3cm 2field is 0.35% and 0.75% for TRD and block tray respectively.