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Modeling the dose dependence of the vis‐absorption spectrum of EBT3 GafChromic™ films
Author(s) -
Callens Maarten B.,
Crijns Wouter,
Depuydt Tom,
Haustermans Karin,
Maes Frederik,
D’Agostino Emiliano,
Wevers Martine,
Pfeiffer Helge,
Van Den Abeele Koen
Publication year - 2017
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 - 10.1002/mp.12246
Subject(s) - materials science , absorption spectroscopy , absorption (acoustics) , absorbance , polymer , irradiation , spectroscopy , analytical chemistry (journal) , dosimetry , spectrometer , absorbed dose , optics , radiation , chemistry , physics , nuclear medicine , medicine , chromatography , quantum mechanics , nuclear physics , composite material
Purpose The aim of this work was to model the dose dependence of the darkening of GafChromic™ EBT 3 films by combining the optical properties of the polydiacetylene polymer phases, and a modified version of the single‐hit model, which will take the stick‐like shape of the monomer microcrystals into account. Second, a comparison is made between the quantification of the film darkening by flatbed scanning and by UV ‐vis absorption spectroscopy. Method GafChromic TM EBT 3 films were irradiated with a 6 MV photon beam at dose levels between 0 and 50 Gy. The radiation‐induced darkening of the films is quantified by a flatbed scanner, and by UV ‐vis absorption spectroscopy in the wavelength range of 220–750 nm. From the UV ‐vis absorption spectra, the contribution of each polymer phase to the absorbance was deduced. Next, the dose dependence of the polymer content is described by a modified single‐hit model where the size distribution of polymerizable centers is approximated by way of the size distribution of the monomer microcrystals in the film. Results The absorption properties of the film can be accurately quantified by UV ‐vis spectroscopy for dose levels between 0 and 10 Gy. Over 10 Gy, the absorption spectrum saturates due to the limited sensitivity of the spectrometer. The modified single‐hit model was successful in describing the increasing polymer concentration with radiation dose, using a log‐normal distribution for the length of the stick‐like monomer microcrystals. The dose dependence of the polymer content, deduced from the UV ‐vis absorption spectrum, differs from that of the flatbed scanning method and is more sensitive to changes in dose. Conclusion The dose dependence of the polymer concentration can be modeled by taking into account the distribution of active centers using the microstructure of the active layer for dose levels between 0 and 10 Gy. The dissimilar dose dependence of the polymer concentration and the absorbance must be accounted for when modeling darkening from the kinetics of the photopolymerization reaction.