Longitudinal Effects in GafChromic® Film Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/n009w500d

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  • Radiochromic film dosimetry offers many advantages over standard film that requires wet chemical processing. Radiochromic film offers: a permanent color change upon irradiation; high spatial resolution; a response that is independent of energy, particle type, and angle of incidence; near tissue equivalence; and a wide dosimetric range. However, there are many notable disadvantages, as well. These include fluctuations that result from: scanner warm-up; temperature history; post-irradiation film darkening; film sensitivity; uniformity discrepancies; and the scanner-lateral effect. The lateral effect occurs as a result of differing angles of polarized light reflecting on mirrors within the scanner. The perceived transmitted light changes with lateral placement on the scanner and is observed more in the red channel due to its longer wavelength and associated increased polarization. Longitudinal effects have not been fully studied, but it is important to determine if longitudinal placement also affects the measured dose. In this study, four 4 X 4 cm² pieces of GafChromic® EBT3 film were irradiated with 100, 300, 500, and 700 cGy. The ODs were measured with FilmQA Pro software at the center of the scanner and at +/- 4, 8, and 12 cm displacement in the longitudinal direction. Triple channel dosimetry was then used to calculate associated doses. Lateral displacement was then briefly studied in an effort to see the dramatic increase in dose with increasing distance from center. The results of this study indicate that a longitudinal effect does exist, but on a much smaller scale than the lateral effect.
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