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      Evaluation of the uncertainty in an EBT3 film dosimetry system utilizing net optical density

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          Abstract

          Radiochromic film has become an important tool to verify dose distributions for intensity‐modulated radiotherapy (IMRT) and quality assurance (QA) procedures. A new radiochromic film model, EBT3, has recently become available, whose composition and thickness of the sensitive layer are the same as those of previous EBT2 films. However, a matte polyester layer was added to EBT3 to prevent the formation of Newton's rings. Furthermore, the symmetrical design of EBT3 allows the user to eliminate side‐orientation dependence. This film and the flatbed scanner, Epson Perfection V750, form a dosimetry system whose intrinsic characteristics were studied in this work. In addition, uncertainties associated with these intrinsic characteristics and the total uncertainty of the dosimetry system were determined. The analysis of the response of the radiochromic film (net optical density) and the fitting of the experimental data to a potential function yielded an uncertainty of 2.6%, 4.3%, and 4.1% for the red, green, and blue channels, respectively. In this work, the dosimetry system presents an uncertainty in resolving the dose of 1.8% for doses greater than 0.8 Gy and less than 6 Gy for red channel. The films irradiated between 0 and 120 Gy show differences in the response when scanned in portrait or landscape mode; less uncertainty was found when using the portrait mode. The response of the film depended on the position on the bed of the scanner, contributing an uncertainty of 2% for the red, 3% for the green, and 4.5% for the blue when placing the film around the center of the bed of scanner. Furthermore, the uniformity and reproducibility radiochromic film and reproducibility of the response of the scanner contribute less than 1% to the overall uncertainty in dose. Finally, the total dose uncertainty was 3.2%, 4.9%, and 5.2% for red, green, and blue channels, respectively. The above uncertainty values were obtained by minimizing the contribution to the total dose uncertainty of the film orientation and film homogeneity.

          PACS number(s): 87.53.Bn

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          Most cited references44

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          Multichannel film dosimetry with nonuniformity correction.

          A new method to evaluate radiochromic film dosimetry data scanned in multiple color channels is presented. This work was undertaken to demonstrate that the multichannel method is fundamentally superior to the traditional single channel method. The multichannel method allows for the separation and removal of the nondose-dependent portions of a film image leaving a residual image that is dependent only on absorbed dose. Radiochromic films were exposed to 10 x 10 cm radiation fields (Co-60 and 6 MV) at doses up to about 300 cGy. The films were scanned in red-blue-green (RGB) format on a flatbed color scanner and measured to build calibration tables relating the absorbed dose to the response of the film in each of the color channels. Film images were converted to dose maps using two methods. The first method used the response from a single color channel and the second method used the response from all three color channels. The multichannel method allows for the separation of the scanned signal into one part that is dose-dependent and another part that is dose-independent and enables the correction of a variety of disturbances in the digitized image including nonuniformities in the active coating on the radiochromic film as well as scanner related artifacts. The fundamental mathematics of the two methods is described and the dose maps calculated from film images using the two methods are compared and analyzed. The multichannel dosimetry method was shown to be an effective way to separate out non-dose-dependent abnormalities from radiochromic dosimetry film images. The process was shown to remove disturbances in the scanned images caused by nonhomogeneity of the radiochromic film and artifacts caused by the scanner and to improve the integrity of the dose information. Multichannel dosimetry also reduces random noise in the dose images and mitigates scanner-related artifacts such as lateral position dependence. In providing an ability to calculate dose maps from data in all the color channels the multichannel method provides the ability to examine the agreement between the color channels. Furthermore, when using calibration data to convert RGB film images to dose using the new method, poor correspondence between the dose calculations for the three color channels provides an important indication that the this new technique enables easy indication in case the dose and calibration films are curve mismatched. The method permit compensation for thickness nonuniformities in the film, increases the signal to noise level, mitigates the lateral dose-dependency of flatbed scanners effect of the calculated dose map and extends the evaluable dose range to 10 cGy-100 Gy. Multichannel dosimetry with radiochromic film like Gafchromic EBT2 is shown to have significant advantages over single channel dosimetry. It is recommended that the dosimetry protocols described be implemented when using this radiochromic film to ensure the best data integrity and dosimetric accuracy.
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            An efficient protocol for radiochromic film dosimetry combining calibration and measurement in a single scan.

            Radiochromic film provides dose measurement at high spatial resolution, but often is not preferred for routine evaluation of patient-specific intensity modulated radiation therapy (IMRT) plans owing to ease-of-use factors. The authors have established an efficient protocol that combines calibration and measurement in a single scan and enables measurement results to be obtained in less than 30 min. This avoids complications due to postexposure changes in radiochromic film that delay the completion of a measurement, often for up to 24 h, in commonly used methods. In addition, the protocol addresses the accuracy and integrity of the measurement by eliminating environmental and interscan variability issues.
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              Radiochromic film dosimetry: recommendations of AAPM Radiation Therapy Committee Task Group 55. American Association of Physicists in Medicine.

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                Author and article information

                Contributors
                oagarciag@innn.edu.mx
                Journal
                J Appl Clin Med Phys
                J Appl Clin Med Phys
                10.1002/(ISSN)1526-9914
                ACM2
                Journal of Applied Clinical Medical Physics
                John Wiley and Sons Inc. (Hoboken )
                1526-9914
                08 September 2016
                September 2016
                : 17
                : 5 ( doiID: 10.1002/acm2.2016.17.issue-5 )
                : 466-481
                Affiliations
                [ 1 ] Laboratorio de Fotomedicina, Biofotónica y Espectroscopia Láser de Pulsos Ultracortos, Facultad de Medicina, Universidad Autónoma del Estado de México Jesús Carranza y Paseo Tollocan s/n. Toluca México
                [ 2 ] Laboratorio de Física Médica, Instituto Nacional de Neurología y Neurocirugía Mexico City México
                [ 3 ] Departamento de Oncología & Departamento de Física y Astronomía Universidad de Calgary Calgary AB Canada
                Author notes
                [*] [* ] aCorresponding author: Olivia Amanda García Garduño, Laboratorio de Física Médica, Instituto Nacional de Neurología y Neurocirugía, Insurgentes Sur 3877, La Fama, Tlalpan, 14269, Mexico City, México; phone: +52 5556063822, ext. 4471, 5021; fax: +52 5556064907; email: oagarciag@ 123456innn.edu.mx

                Article
                ACM20001X
                10.1120/jacmp.v17i5.6262
                5874103
                27685125
                00b4019e-b17f-43c3-88e3-1c0aa151c470
                © 2016 The Authors.

                This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                History
                : 14 December 2015
                : 16 May 2016
                Page count
                Figures: 10, Tables: 1, References: 48, Pages: 16, Words: 7299
                Categories
                Radiation Measurements
                Radiation Measurements
                Custom metadata
                2.0
                acm20001x
                September 2016
                Converter:WILEY_ML3GV2_TO_NLMPMC version:5.2.5 mode:remove_FC converted:16.11.2017

                radiochromic film,flatbed scanner,dosimetry,uncertain analysis

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