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MO‐E‐BRA‐06: Dose Response of MD‐55, EBT and EBT‐2 Radiochromic Films: A Monte Carlo Study
Author(s) -
Chibani O
Publication year - 2010
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 - 10.1118/1.3469109
Subject(s) - materials science , monte carlo method , photon , dosimetry , electron , analytical chemistry (journal) , optics , nuclear medicine , physics , chemistry , nuclear physics , medicine , statistics , mathematics , chromatography
Purpose : To calculate the film dose response using Monte Carlo simulation of photon/electron transport. The film dose response (dose in film versus dose in water) is calculated for brachytherapy sources ( 103 Pd, 125 I, 192 Ir and 137 Cs) and megavoltage photons beams ( 60 Co, 6 MV and 18 MV). Effects of the film composition and source‐film distance on the film response are also investigated. Material and Methods : The GEPTS code is used for dose calculations in radiochromic films. The detailed film structure including the film base, the adhesive, the surface layer, and the active layer is simulated. The elemental compositions of these layers are provided by the manufacturer. Photons and electrons are transported down to 1 keV. The GEPTS photoionization and atomic relaxation processes are based on the latest EPDL97 cross section database. Results : The film response is very sensitive to variations of the elemental composition of the active layer. Up to 100% differences are seen between MD‐55, EBT and EBT‐2. For a given film, variations in Cl, K and Br (which contents are normally below 0.3%) can have major effects on the film response for barchytherapy sources (e.g. 103 Pd, 125 I and 192 Ir). Increased source‐film distance can lead to non‐negligible variations of the dose response because of energy spectrum hardening (e.g. 3% for 103 Pd at 8 cm versus 2 cm from the film). For 60 Co, 6 MV and 18 MV beams, the film dose response is very close to unity even in the buildup region. Conclusion : Although the energy deposited in film is not simply related to the measured optical density, it is nevertheless important to understand how it compares with the dose in water for different energies and irradiation setups. Present calculations are the first step towards a more comprehensive study involving the chemistry and physics of radiochromic films (e.g. percolation theory).