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Optical characterization of a radiochromic film by total reflectance and transmittance measurements
Author(s) -
Fusi Franco,
Mercatelli Luca,
Marconi Giacomo,
Cuttone Giacomo,
Romano Giovanni
Publication year - 2004
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 - 10.1118/1.1764701
Subject(s) - transmittance , materials science , absorbance , scattering , optics , absorption (acoustics) , attenuation coefficient , integrating sphere , densitometer , wavelength , photon , light scattering , irradiation , analytical chemistry (journal) , optoelectronics , chemistry , physics , chromatography , nuclear physics
The GafChromic™ film (GCF) MD‐55‐2, a radiochromic material, was examined for its optical properties through total reflectance and transmittance measurements in visible spectrum (400–700 nm). By using a multilayer model of the film and Kubelka–Munk's (KM) theory, absorption and scattering coefficients of the film sensitive layer ( K and S , respectively) were obtained from measurements of irradiated and nonirradiated slides. This has allowed calculation of the absorbance A KMof the sensitive layer of the GCF. The model easily splits scattering from absorption. Unlike absorption, scattering is essentially insensitive to irradiation dose and decreases slowly as the wavelength increases. The scattering effect is predominant over absorption in the 400–500 nm range, while beyond 600 nm absorption prevails. The A KMabsorbance of the sensitive layer was calculated using the K coefficient and compared with the optical densities (OD) measured considering only ballistic photons (as in a standard spectrophotometer) as well as the optical densities measured collecting all the transmitted photons (as in many densitometers). The values of A KMfound were always lower than OD measured by the other methods and they had the best linearity on the whole visible range. These data support the hypothesis that the sensitive layer reacts to irradiation more linearly than that shown by measurements using standard commercial devices. However, in the 600–680 nm range, correction is not very important because absorption is predominant over scattering. When GCF is used for imaging, scattering produces a loss of spatial information. Consequently, it is necessary to collect only ballistic photons and to correct absorbance by K and S coefficients.