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Luis Isaac Ramos Garcia

Bio: Luis Isaac Ramos Garcia is an academic researcher from University of Navarra. The author has contributed to research in topics: Dosimetry & Polarizer. The author has an hindex of 3, co-authored 8 publications receiving 99 citations.

Papers
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Journal ArticleDOI
TL;DR: A new method to extract the electron density and the effective atomic number from dual-energy CT images, based on a Karhunen-Loeve expansion of the atomic cross section per electron, which was used to calibration a Siemens Definition CT using the CIRS phantom.
Abstract: The purpose of this work is to present a new method to extract the electron density () and the effective atomic number (Z eff) from dual-energy CT images, based on a Karhunen-Loeve expansion (KLE) of the atomic cross section per electron. This method was used to calibrate a Siemens Definition CT using the CIRS phantom. The predicted electron density and effective atomic number using 80 kVp and 140 kVp were compared with a calibration phantom and an independent set of samples. The mean absolute deviations between the theoretical and calculated values for all the samples were 1.7 % ± 0.1 % for and 4.1 % ± 0.3 % for Z eff. Finally, these results were compared with other stoichiometric method. The application of the KLE to represent the atomic cross section per electron is a promising method for calculating and Z eff using dual-energy CT images.

48 citations

Journal ArticleDOI
TL;DR: The improved multichannel dosimetric method is able to remove many of the common disturbances usually present in radiochromic films and improves the gamma analysis results compared with the other three methods.
Abstract: Purpose: An improved method for multichannel dosimetry is presented. This method explicitly takes into account the information provided by the unexposed image of the film. Methods: The method calculates the dose by applying a couple of perturbations to the scanned dose, one dependent and the other independent on the color channel. The method has been compared with previous multichannel and two single channel methods (red and green) against measurements using two different tests: first, five percentage depth dose profiles covering a wide range of doses; second, the dose map perpendicular to the beam axis for a 15 × 15cm 2 square field. Finally, the results of 30 IMRT quality assurances tests are presented. All tests have been evaluated using the gamma analysis. Results: The coefficient of variation was found to be similar for all methods in a wide range of doses. The results of the proposed method are more in agreement with the experimental measurements and with the treatment planning system. Furthermore, the differences in the mean gamma pass rates are statistically significant. Conclusions: The improved multichannel dosimetric method is able to remove many of the common disturbances usually present in radiochromic films and improves the gamma analysis results compared with the other three methods.

42 citations

Journal ArticleDOI
TL;DR: Methods that take into account all the variability both in dose and in optical density should be used in the calibration process, according to the results of the simulations.
Abstract: Purpose: To compare how the inclusion of the uncertainties in dose and optical density affects the results of the calibration of Gafchromic® EBT3 radiochromic films. Methods: Five methods of least square minimization were compared for calibration of radiochromic films. These differed in the way in which the uncertainties of dose and optical density are taken into account. The comparison was made by simulating the calibration fit at an increasing number of points measured in the calibration table and in the gamma analysis of ten real IMRT verifications. Results: According to the results of the simulations, the methods that take into account all the variability in dose and optical density are superior to those that do not use them. The improvements are reflected in lower bias of the parameters, lower variability and faster convergence when the number of the points increases in the calibration table. When these methods are employed in the gamma analysis comparison, the statistical significance of the results depends on how restrictive the parameters are that define this comparison. Conclusions: Methods that take into account all the variability both in dose and in optical density should be used in the calibration process.

17 citations

Journal ArticleDOI
TL;DR: Using a polarized film with the polarization axis parallel to the coating direction of the radiochromic film, and preferably above it, significantly improves the dosimetry results and is an easy and inexpensive way to correct the lateral artifacts of the conventional EBT3 dosimetric.

3 citations


Cited by
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Journal ArticleDOI
TL;DR: This review focuses on dual-energy CT imaging including related issues of radiation exposure to patients, scanning and post-processing options, and potential clinical benefits mainly to improve the understanding of clinical radiologists and thus, expand the clinical use of dual- energy CT.
Abstract: Dual-energy CT has remained underutilized over the past decade probably due to a cumbersome workflow issue and current technical limitations Clinical radiologists should be made aware of the potential clinical benefits of dual-energy CT over single-energy CT To accomplish this aim, the basic principle, current acquisition methods with advantages and disadvantages, and various material-specific imaging methods as clinical applications of dual-energy CT should be addressed in detail Current dual-energy CT acquisition methods include dual tubes with or without beam filtration, rapid voltage switching, dual-layer detector, split filter technique, and sequential scanning Dual-energy material-specific imaging methods include virtual monoenergetic or monochromatic imaging, effective atomic number map, virtual non-contrast or unenhanced imaging, virtual non-calcium imaging, iodine map, inhaled xenon map, uric acid imaging, automatic bone removal, and lung vessels analysis In this review, we focus on dual-energy CT imaging including related issues of radiation exposure to patients, scanning and post-processing options, and potential clinical benefits mainly to improve the understanding of clinical radiologists and thus, expand the clinical use of dual-energy CT; in addition, we briefly describe the current technical limitations of dual-energy CT and the current developments of photon-counting detector

232 citations

Journal ArticleDOI
TL;DR: This review summarizes technical aspects associated with the establishment of reference radiochromic film dosimetry and its subsequent use for either clinical or research applications.

214 citations

Journal ArticleDOI
TL;DR: This Task Group report provides a basic understanding of available RCF models, dosimetric characteristics and properties, advantages and limitations, configurations, and overall elemental compositions of the RCFs that have changed over the past 20 years.
Abstract: The use of radiochromic film (RCF) dosimetry in radiation therapy is extensive due to its high level of achievable accuracy for a wide range of dose values and its suitability under a variety of measurement conditions. However, since the publication of the 1998 AAPM Task Group 55, Report No. 63 on RCF dosimetry, the chemistry, composition, and readout systems for RCFs have evolved steadily. There are several challenges in using the new RCFs, readout systems and validation of the results depending on their applications. Accurate RCF dosimetry requires understanding of RCF selection, handling and calibration methods, calibration curves, dose conversion methods, correction methodologies as well as selection, operation and quality assurance (QA) programs of the readout systems. Acquiring this level of knowledge is not straight forward, even for some experienced users. This Task Group report addresses these issues and provides a basic understanding of available RCF models, dosimetric characteristics and properties, advantages and limitations, configurations, and overall elemental compositions of the RCFs that have changed over the past 20 yr. In addition, this report provides specific guidelines for data processing and analysis schemes and correction methodologies for clinical applications in radiation therapy.

110 citations

Journal ArticleDOI
TL;DR: Calibration curves at the different lateral positions could be correlated by a simple two-point rescaling using the response for unexposed film as well as the response of film exposed at high doses between 800 and 1600 cGy.
Abstract: Purpose: A known factor affecting the accuracy of radiochromic film dosimetry is the lateral response artifact (LRA) induced by nonuniform response of a flatbed scanner in the direction perpendicular to the scan direction. This work reports a practical solution to eliminate such artifacts for all forms of dose QA. Methods: EBT3 films from a single production lot (02181401) cut into rectangular 4 × 5 cm2 pieces, with the long dimension parallel to the long dimension of the original 20.3 × 25.4 cm2 sheets, were exposed at a depth of 5 cm on a Varian Trilogy at the center of a 20 × 20 cm2 open field at seven doses between 50 and 1600 cGy using 6 MV photons. These films together with an unexposed film from the same production lot were lined one next to the other on an Epson 10000XL or 11000XL scanner in portrait orientation with their long dimension parallel to the scan direction. Scanned images were then obtained with the line of films positioned at seven discrete lateral locations perpendicular to the scan direction. The process was repeated in landscape orientation and on three other Epson scanners. Data were also collected for three additional production lots of EBT3 film (11051302, 03031401, and 03171403). From measurements at the various lateral positions, the scanner response was determined as a function of the lateral position of the scanned film. For a given color channel X, the response at any lateral position L is related to the response at the center, C, of the scanner by Response(C, D, X) = A L,X + B L,X ⋅Response(L, D, X), where D is dose and the coefficients A L,X and B L,X are determined from the film measurements at the center of the scanner and six other discrete lateral positions. The values at intermediate lateral positions were obtained by linear interpolation. The coefficients were determined for the red, green, and blue color channels, preserving the ability to apply triple-channel dosimetry once corrections were applied to compensate for the lateral position response artifact. To validate this method, corrections were applied to several films that were exposed to 15 × 15cm2 open fields and large IMRT and VMAT fields and scanned at the extreme edges of the scan window in addition to the central location. Calibration and response data were used to generate dose maps and perform gamma analysis using single- or triple-channel dosimetry with FilmQAPro 2014 software. Results: The authors’ study found that calibration curves at the different lateral positions could be correlated by a simple two-point rescaling using the response for unexposed film as well as the response of film exposed at high doses between 800 and 1600 cGy. The coefficients A L,X and B L,X for each color channel X were found to be independent of dose at each lateral location L. This made it possible to apply the relationship Response(C, D, X) = A L,X + B L,X ⋅Response(L, D, X), to the raw film responses, permitting correction of the response values at any lateral position to an equivalent response, as if that part of the film was located at the center of the scanner. This correction method was validated for several films exposed to open as well as large IMRT and VMAT fields. Conclusions: The work reported elaborates on the process using the correction procedures to eliminate the lateral response artifact and demonstrates improvements in the accuracy of radiochromic film dosimetry for the radiation therapy quality assurance applications.

82 citations

Journal ArticleDOI
TL;DR: Dosimetry of ionising radiation is a well-established and mature branch of physical sciences with many applications in medicine and biology and two fundamental issues remain: the accuracy of the measurement from a scientific perspective and the importance to link the measurement to a clinically relevant question.
Abstract: Dosimetry of ionising radiation is a well-established and mature branch of physical sciences with many applications in medicine and biology. In particular radiotherapy relies on dosimetry for optimisation of cancer treatment and avoidance of severe toxicity for patients. Several novel developments in radiotherapy have introduced new challenges for dosimetry with small and dynamically changing radiation fields being central to many of these applications such as stereotactic ablative body radiotherapy and intensity modulated radiation therapy. There is also an increasing awareness of low doses given to structures not in the target region and the associated risk of secondary cancer induction. Here accurate dosimetry is important not only for treatment optimisation but also for the generation of data that can inform radiation protection approaches in the future. The article introduces some of the challenges and highlights the interdependence of dosimetric calculations and measurements. Dosimetric concepts are explored in the context of six application fields: reference dosimetry, small fields, low dose out of field, in vivo dosimetry, brachytherapy and auditing of radiotherapy practice. Recent developments of dosimeters that can be used for these purposes are discussed using spatial resolution and number of dimensions for measurement as sorting criteria. While dosimetry is ever evolving to address the needs of advancing applications of radiation in medicine two fundamental issues remain: the accuracy of the measurement from a scientific perspective and the importance to link the measurement to a clinically relevant question. This review aims to provide an update on both of these.

80 citations