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SU‐E‐T‐120: Characterization of EBT2 Film for Absolute Dosimetry in Proton Beams
Author(s) -
Devaraju V,
Slopsema R
Publication year - 2011
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 - 10.1118/1.3612071
Subject(s) - sobp , materials science , dosimetry , imaging phantom , bragg peak , calibration , optics , scanner , reproducibility , ionization chamber , calibration curve , dose profile , percentage depth dose curve , proton therapy , beam (structure) , scattering , proton , nuclear medicine , physics , ionization , nuclear physics , chemistry , medicine , ion , chromatography , quantum mechanics , detection limit
Purpose: The objective of this work is to fully characterize Gafchromic EBT2 film for absolute dose measurement (in‐vitro and in‐vivo) in the spread out Bragg peak (SOBP) of both scanned and scattered proton beams. Methods and Materials: The OD‐vs‐dose calibration curve is determined by irradiating film at different depths (0, 5, 10, 15, 20, and 25 cm) to different dose in a calibration field (range 28 g/cm2, modulation 15 g/cm2). Solid water slabs are used as phantom; 4x5 cm films are irradiated to nine dose levels spanning from 10 cGy to 1000 cGy. Beam output is measured using parallel plate ionization chamber both to calculate the specific doses delivered to the film and to compare the measured dose with the calculated dose from the film. The films are digitized with EPSON scanner and the net optical density computed. Measurement done at different depths (different average energy) are combined to create a single calibration curve. Verification measurements are performed for different range and modulation combinations, at various depths, and using both double‐scattering and uniform‐scanning delivery, thus validating the use of single sensitometric plot for different proton energy and delivery technique. In addition, reproducibility, angular response, and film uniformity are investigated. Results: Using the single calibration curve, the accuracy of absolute dose measurements using EBT2 film is found to be within 5% for any point within the SOBP excluding the distal fall off region and at very low dose level (<15cGy). No difference in response to scattering or scanning beams is observed. The day‐to‐day reproducibility is better than 1%. The uncertainty introduced by angular response, film nonuniformity and different delivery techniques are found to be insignificant. Conclusions: EBT2 film is a viable option for absolute dose measurements both for in‐vitro and in‐vivo.