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Slobodan Devic - One of the best experts on this subject based on the ideXlab platform.
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Comparison of dose response functions for EBT3 model GafChromic™ Film Dosimetry system.
Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Associ, 2018Co-Authors: Saad Aldelaijan, Slobodan DevicAbstract:Abstract Objective Different dose response functions of EBT3 model GafChromic™ Film Dosimetry system have been compared in terms of sensitivity as well as uncertainty vs. error analysis. We also made an assessment of the necessity of scanning Film pieces before and after irradiation. Methods Pieces of EBT3 Film model were irradiated to different dose values in Solid Water (SW) phantom. Based on images scanned in both reflection and transmission mode before and after irradiation, twelve different response functions were calculated. For every response function, a reference radiochromic Film Dosimetry system was established by generating calibration curve and by performing the error vs. uncertainty analysis. Results Response functions using pixel values from the green channel demonstrated the highest sensitivity in both transmission and reflection mode. All functions were successfully fitted with rational functional form, and provided an overall one-sigma uncertainty of better than 2% for doses above 2 Gy. Use of pre-scanned images to calculate response functions resulted in negligible improvement in dose measurement accuracy. Conclusion Although reflection scanning mode provides higher sensitivity and could lead to a more widespread use of radiochromic Film Dosimetry, it has fairly limited dose range and slightly increased uncertainty when compared to transmission scan based response functions. Double-scanning technique, either in transmission or reflection mode, shows negligible improvement in dose accuracy as well as a negligible increase in dose uncertainty. Normalized pixel value of the images scanned in transmission mode shows linear response in a dose range of up to 11 Gy.
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Reference radiochromic Film Dosimetry: Review of technical aspects
Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Associ, 2016Co-Authors: Slobodan Devic, Nada Tomic, David LewisAbstract:For decades, Film was used as a powerful two-dimensional (2D) Dosimetry tool for radiotherapy treatment verification and quality assurance. Unlike the old silver-halide based radiographic Films, radiochromic Films change its color upon irradiation without the need for chemical development. Radiation dose deposited within a sensitive layer of the radiochromic Film initiates polymerization of the active component, the degree of which depends on the amount of energy deposited. Response of the Film to radiation is commonly expressed in terms of optical density change, which can be easily measured by any photometric device. However, a number of factors may have an impact on the signal detected by the measuring device. This review summarizes technical aspects associated with the establishment of reference radiochromic Film Dosimetry and its subsequent use for either clinical or research applications.
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A protocol for EBT3 radiochromic Film Dosimetry using reflection scanning.
Medical physics, 2014Co-Authors: P Papaconstadopoulos, Jan Seuntjens, Gyorgy Hegyi, Slobodan DevicAbstract:Purpose: To evaluate the performance of the EBT3 radiochromic Film Dosimetry system using reflection measurements and to suggest a calibration protocol for precise and accurate reflection Film Dosimetry. Methods: A set of 14 Gafchromic EBT3 Film pieces were irradiated to various doses ranging from 0 to 8 Gy and subsequently scanned using both the reflection and transmission mode. Scanning resolution varied from 50 to 508 dpi (0.5–0.05 mm/pixel). Both the red and green color channels of scanned images were used to relate the Film response to the dose. A sensitivity, uncertainty, and accuracy analysis was performed for all scanning modes and color channels. The total uncertainty, along with the fitting and experimental uncertainty components, was identified and analyzed. A microscope resolution target was used to evaluate possible resolution losses under reflection scanning. The calibration range was optimized for reflection scanning in the low ( 2 Gy) dose regions based on the reported results. Results: Reflection scanning using the red channel exhibited the highest sensitivity among all modes, being up to 150% higher than transmission mode in the red channel for the lowest dose level. Furthermore, there was no apparent loss in resolution between the two modes. However, higher uncertainties and reduced accuracy were observed for the red channel under reflection mode, especially at dose levels higher than 2 Gy. These uncertainties were mainly attributed to saturation effects which were translated in poor fitting results. By restricting the calibration to the 0–2 Gy dose range, the situation is reversed and the red reflection mode was superior to the transmission mode. For higher doses, the green channel in reflection mode presented comparable results to the red transmission. Conclusions: A two-color reflection scanning protocol can be suggested for EBT3 radiochromic Film Dosimetry using the red channel for doses less than 2 Gy and the green channel for higher doses. The precision and accuracy are significantly improved in the low dose region following such a protocol.
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characterization of calibration curves and energy dependence gafchromictm xr qa2 model based radiochromic Film Dosimetry system
Medical Physics, 2014Co-Authors: N Tomic, Saad Aldelaijan, Chrystian Quintero, Bruce R Whiting, Hamed Bekerat, Liheng Liang, F Deblois, J Seuntjens, Slobodan DevicAbstract:Purpose: The authors investigated the energy response of XR-QA2 GafChromicTM Film over a broad energy range used in diagnostic radiology examinations. The authors also made an assessment of the most suitable functions for both reference and relative dose measurements. Methods: Pieces of XR-QA2 Film were irradiated to nine different values of air kerma in air, following reference calibration of a number of beam qualities ranging in HVLs from 0.16 to 8.25 mm Al, which corresponds to effective energy range from 12.7 keV to 56.3 keV. For each beam quality, the authors tested three functional forms (rational, linear exponential, and power) to assess the most suitable function by fitting the delivered air kerma in air as a function of Film response in terms of reflectance change. The authors also introduced and tested a new parameterχ = netΔR·em netΔR that linearizes the inherently nonlinear response of the Film. Results: The authors have found that in the energy range investigated, the response of the XR-QA2 based radiochromic Film Dosimetry system ranges from 0.222 to 0.420 in terms of netΔR at K air air = 8 cGy. For beam qualities commonly used in CT scanners (4.03–8.25 mm Al), the variation in Film response (netΔR at K air air = 8 cGy) amounts to ± 5%, while variation in K air air amounts to ± 14%. Conclusions: Results of our investigation revealed that the use of XR-QA2 GafChromicTM Film is accompanied by a rather pronounced energy dependent response for beam qualities used for x-ray based diagnostic imaging purposes. The authors also found that the most appropriate function for the reference radiochromic Film Dosimetry would be the power function, while for the relative Dosimetry one may use the exponential response function that can be easily linearized.
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Linearization of dose-response curve of the radiochromic Film Dosimetry system.
Medical physics, 2012Co-Authors: Slobodan Devic, Nada Tomic, Saad Aldelaijan, François Deblois, Jan Seuntjens, Maria F. Chan, Dave LewisAbstract:Purpose: Despite numerous advantages of radiochromic Film dosimeter (high spatial resolution, near tissue equivalence, low energy dependence) to measure a relative dose distribution with Film, one needs to first measure an absolute dose (following previously established reference Dosimetry protocol) and then convert measured absolute dose values into relative doses. In this work, we present result of our efforts to obtain a functional form that would linearize the inherently nonlinear dose–response curve of the radiochromic Film Dosimetry system. Methods: Functional form [ ζ = (−1)·netOD(2/3)/ln(netOD)] was derived from calibration curves of various previously established radiochromic Film Dosimetry systems. In order to test the invariance of the proposed functional form with respect to the Film model used we tested it with three different GAFCHROMIC™ Film models (EBT, EBT2, and EBT3) irradiated to various doses and scanned on a same scanner. For one of the Film models (EBT2), we tested the invariance of the functional form to the scanner model used by scanning irradiated Film pieces with three different flatbed scanner models (Epson V700, 1680, and 10000XL). To test our hypothesis that the proposed functional argument linearizes the response of the radiochromic Film Dosimetry system, verification tests have been performed in clinical applications: percent depth dose measurements, IMRT quality assurance (QA), and brachytherapy QA. Results: Obtained R2 values indicate that the choice of the functional form of the new argument appropriately linearizes the dose response of the radiochromic Film Dosimetry system we used. The linear behavior was insensitive to both Film model and flatbed scanner model used. Measured PDD values using the green channel response of the GAFCHROMIC™ EBT3 Film model are well within ±2% window of the local relative dose value when compared to the tabulated Cobalt-60 data. It was also found that criteria of 3%/3 mm for an IMRT QA plan and 3%/2 mm for a brachytherapy QA plan are passing 95% gamma function points. Conclusions: In this paper, we demonstrate the use of functional argument to linearize the inherently nonlinear response of a radiochromic Film based reference Dosimetry system. In this way, relative Dosimetry can be conveniently performed using radiochromic Film Dosimetry system without the need of establishing calibration curve.
C. De Wagter - One of the best experts on this subject based on the ideXlab platform.
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A method of increasing the Film intrinsic robustness of radiochromic Film Dosimetry.
Physics in medicine and biology, 2012Co-Authors: A. Ngwa Ebongue, R. P. Srivastava, M.g. Kwato Njock, C. De WagterAbstract:The radiochromic Film, which is used, in combination with a flatbed scanner has become a widely used tool for a quantitative evaluation of radiation dose in radiation therapy. One aspect of uncertainty using the radiochromic Film is the magnitude of orientation effects when the orientation of the Film is not kept constant during the digitization process. The aim of this note was to investigate the impact of using a combination of two crossed sheets of EBT2 Film on various aspects of radiochromic Film Dosimetry. First the impact on the Film sensitivity was studied. We also investigated the influence on orientation effects during scanning. The results show that the double crossed Film combination increases the sensitivity with a factor 1.7-2.1 and practically eliminates the effects of Film orientation on the optical density read-out and the lateral correction profiles.
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Evaluation of a glassless photographic Film scanner for high-gradient radiochromic Film Dosimetry
Physics in medicine and biology, 2011Co-Authors: A. De Puysseleyr, R. P. Srivastava, Leen Paelinck, W. De Neve, C. De WagterAbstract:This study evaluates the performance of the Nikon Coolscan 9000 ED Film scanner for high-gradient radiochromic Film Dosimetry. As a reference for comparison, analogue experiments were performed on the Epson Expression 10000XL flatbed scanner. Based on these results, a dosimetric protocol was established for the Nikon scanner and its overall performance for high-gradient Dosimetry was evaluated. The Nikon scanner demonstrated a high sensitivity for radiochromic Film Dosimetry, resulting in more contrast in the digitized image. The scanner's optics also demonstrated excellent stability and did not necessitate warm-up scans prior to data acquisition. Moreover, negative effects of temperature changes of the Film inside the scanner were shown to be limited. None of the digitized images showed significant disturbances by moire-patterns, by virtue of the absence of a glass plate for Film positioning. However, scanner response was found to vary considerably across the reading area, requiring an optical density-dependent correction procedure to be incorporated into the scanning protocol. The main limitation of the Nikon Coolscan 9000 ED transmission scanner remains its Film size restriction to 6.2 × 20 cm2. Nevertheless, its excellent characteristics render it the preferential tool for high-gradient radiochromic Film Dosimetry in applications limited to small Film sizes, such as Dosimetry in the build-up region.
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The value of EDR2 Film Dosimetry in compensator-based intensity modulated radiation therapy
Physics in medicine and biology, 2007Co-Authors: R. P. Srivastava, C. De WagterAbstract:Radiographic or silver halide Film is a well-established 2D dosimeter with an unquestioned spatial resolution. But its higher sensitivity to low-energy photons has to be taken into consideration. Metal compensators or physical modulators to deliver intensity modulated radiation therapy (IMRT) are known to change the beam energy spectrum and to produce scattered photons and contaminating electrons. Therefore the reliability of Film Dosimetry in compensator-based IMRT might be questioned. Conflicting data have been reported in the literature. This uncertainty about the validity of Film Dosimetry in compensator-based IMRT triggered us to conduct this study. First, the effect of MCP-96 compensators of varying thickness on the depth dose characteristics was investigated using a diamond detector which has a uniform energy response. A beam hardening effect was observed at 6 MV that resulted in a depth dose increase that remained below 2% at 20 cm depth. At 25 MV, in contrast, beam softening produced a dose decrease of up to 5% at the same depth. Second, dose was measured at depth using EDR2 Film in perpendicular orientation to both 6 MV and 25 MV beams for different compensator thicknesses. A Film dose underresponse of 1.1% was found for a 30 mm thick block in a 25 MV beam, which realized a transmission factor of 0.243. The effect induced by the compensators is higher than the experimental error but still within the accepted overall uncertainty of Film Dosimetry in clinical IMRT QA. With radiographic Film as an affordable QA tool, the physical compensator remains a low threshold technique to deliver IMRT.
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Precautions and strategies in using a commercial flatbed scanner for radiochromic Film Dosimetry.
Physics in medicine and biology, 2006Co-Authors: Leen Paelinck, W. De Neve, C. De WagterAbstract:The purpose of this study was to investigate the value of a commercially available flatbed scanner for Film Dosimetry with radiochromic Film for external radiotherapy. The EPSON Pro 1680 Expression scanner was examined as a densitometer for two-dimensional Film Dosimetry with Gafchromic EBT Film. An accurate and efficient scanning procedure was established. Possible drift and warm-up effects of the scanner were studied and the direct physical influence of the scanner light on the radiochromic Film was assessed. Next, we investigated the scan field uniformity. Also, we examined if the accuracy of radiochromic Film was improved by subtracting the optical density of the unirradiated blank Film from the optical density of the irradiated Film. To assess the accuracy of Gafchromic EBT Film when the EPSON scanner was used as a densitometer, the depth dose of a 2 × 15 cm2 field and the in-plane and cross-plane profiles of a 15 × 15 cm2 field were measured and compared with diamond detector measurements. When taking consecutive scans, we found that the optical density taken from the first scan was about 1% higher than the optical density taken from subsequent scans. We attribute this to the warming up of the lamp of the scanner. Longer-term drift of the scanner was found to be absent. We found that the use of a correction matrix was necessary to correct for the non-uniform scanner response over the scan field. Subtracting the optical density of the unirradiated blank Film from the irradiated Film improves the precision of the Gafchromic EBT Film. Depth dose and profile measurements with Gafchromic EBT Film and the diamond detector are in agreement within 2.5%. The EPSON Pro 1680 Expression scanner is an excellent tool for accurate two-dimensional Film Dosimetry with Gafchromic EBT Film provided that some precautions and corrections are taken into account.
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Characteristics of a commercially available Film digitizer and their significance for Film Dosimetry
Physics in medicine and biology, 1998Co-Authors: B. Mersseman, C. De WagterAbstract:Dosimetric detectors used in high-energy photon radiation Dosimetry mainly perform a zero- or one-dimensional measurement. These low-dimensional methods are not always adequate in the context of conformal radiotherapy. Therefore, two-dimensional Film Dosimetry has attracted attention. We studied a 12-bit CCD-based Film digitizer (Vidar VXR-12) with regard to accurate Film Dosimetry. We investigated the stability, linearity, noise, effects of aberrant light scatter and built-in conversion tables. A digitizing resolution of 75 dpi and a digitizing speed of 20 ms/line result in an optimal signal-to-noise ratio. At optical densities above 2.0, the reading accuracy of the digitizer is limited by noise. The results of various experiments prove both the capabilities and limitations of the digitizer studied. We also propose a method to acquire and process Film data using such a digitizer.
Jan Seuntjens - One of the best experts on this subject based on the ideXlab platform.
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A protocol for EBT3 radiochromic Film Dosimetry using reflection scanning.
Medical physics, 2014Co-Authors: P Papaconstadopoulos, Jan Seuntjens, Gyorgy Hegyi, Slobodan DevicAbstract:Purpose: To evaluate the performance of the EBT3 radiochromic Film Dosimetry system using reflection measurements and to suggest a calibration protocol for precise and accurate reflection Film Dosimetry. Methods: A set of 14 Gafchromic EBT3 Film pieces were irradiated to various doses ranging from 0 to 8 Gy and subsequently scanned using both the reflection and transmission mode. Scanning resolution varied from 50 to 508 dpi (0.5–0.05 mm/pixel). Both the red and green color channels of scanned images were used to relate the Film response to the dose. A sensitivity, uncertainty, and accuracy analysis was performed for all scanning modes and color channels. The total uncertainty, along with the fitting and experimental uncertainty components, was identified and analyzed. A microscope resolution target was used to evaluate possible resolution losses under reflection scanning. The calibration range was optimized for reflection scanning in the low ( 2 Gy) dose regions based on the reported results. Results: Reflection scanning using the red channel exhibited the highest sensitivity among all modes, being up to 150% higher than transmission mode in the red channel for the lowest dose level. Furthermore, there was no apparent loss in resolution between the two modes. However, higher uncertainties and reduced accuracy were observed for the red channel under reflection mode, especially at dose levels higher than 2 Gy. These uncertainties were mainly attributed to saturation effects which were translated in poor fitting results. By restricting the calibration to the 0–2 Gy dose range, the situation is reversed and the red reflection mode was superior to the transmission mode. For higher doses, the green channel in reflection mode presented comparable results to the red transmission. Conclusions: A two-color reflection scanning protocol can be suggested for EBT3 radiochromic Film Dosimetry using the red channel for doses less than 2 Gy and the green channel for higher doses. The precision and accuracy are significantly improved in the low dose region following such a protocol.
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Linearization of dose-response curve of the radiochromic Film Dosimetry system.
Medical physics, 2012Co-Authors: Slobodan Devic, Nada Tomic, Saad Aldelaijan, François Deblois, Jan Seuntjens, Maria F. Chan, Dave LewisAbstract:Purpose: Despite numerous advantages of radiochromic Film dosimeter (high spatial resolution, near tissue equivalence, low energy dependence) to measure a relative dose distribution with Film, one needs to first measure an absolute dose (following previously established reference Dosimetry protocol) and then convert measured absolute dose values into relative doses. In this work, we present result of our efforts to obtain a functional form that would linearize the inherently nonlinear dose–response curve of the radiochromic Film Dosimetry system. Methods: Functional form [ ζ = (−1)·netOD(2/3)/ln(netOD)] was derived from calibration curves of various previously established radiochromic Film Dosimetry systems. In order to test the invariance of the proposed functional form with respect to the Film model used we tested it with three different GAFCHROMIC™ Film models (EBT, EBT2, and EBT3) irradiated to various doses and scanned on a same scanner. For one of the Film models (EBT2), we tested the invariance of the functional form to the scanner model used by scanning irradiated Film pieces with three different flatbed scanner models (Epson V700, 1680, and 10000XL). To test our hypothesis that the proposed functional argument linearizes the response of the radiochromic Film Dosimetry system, verification tests have been performed in clinical applications: percent depth dose measurements, IMRT quality assurance (QA), and brachytherapy QA. Results: Obtained R2 values indicate that the choice of the functional form of the new argument appropriately linearizes the dose response of the radiochromic Film Dosimetry system we used. The linear behavior was insensitive to both Film model and flatbed scanner model used. Measured PDD values using the green channel response of the GAFCHROMIC™ EBT3 Film model are well within ±2% window of the local relative dose value when compared to the tabulated Cobalt-60 data. It was also found that criteria of 3%/3 mm for an IMRT QA plan and 3%/2 mm for a brachytherapy QA plan are passing 95% gamma function points. Conclusions: In this paper, we demonstrate the use of functional argument to linearize the inherently nonlinear response of a radiochromic Film based reference Dosimetry system. In this way, relative Dosimetry can be conveniently performed using radiochromic Film Dosimetry system without the need of establishing calibration curve.
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TH‐E‐BRB‐02: Linearization of Dose Response Curve for the Radiochromic Film Dosimetry System
Medical Physics, 2012Co-Authors: Dave Lewis, Slobodan Devic, Nada Tomic, Saad Aldelaijan, François Deblois, Maria F. Chan, Jan SeuntjensAbstract:Purpose: In order to measure relative dose distribution with radiochromic Film, one need to first measure an absolute dose (following previously established reference Dosimetry protocol) and then convert measured absolute dose into relative dose. We present here result of our efforts to establish a functional form that converts the inherently non‐linear dose response curve of the radiochromic Film Dosimetry system into liner one. Methods: In order to test the invariance of the proposed functional form with respect to the Film or scanner model used, we have tested it on Film pieces from three different GAFCHROMICTM Film models (EBT, EBT‐2, and EBT‐3) irradiated to various doses and scanned on a single scanner. for one of the Film models we have also tested it by scanning with three different flatbed scanner models (Epson V700, 1680, and 10000XL). To test our hypothesis that the proposed functional argument linearizes the response of the radiochromic Film Dosimetry system, we performed a measurement of percent depth dose (PDD) curves in Cobalt‐60 beam. Results: Obtained R2 values indicate that the choice of the functional form of the new argument (ζ) appropriately linearizes the dose response of the radiochromic Film Dosimetry system we used. The linear behavior was insensitive to both Film model and flatbed scanner model used. Measured PDD values using the green channel response of the GAFCHROMICTM EBT‐3 Film model are well within ±2% window of the local relative dose value when compared to the tabulated Cobalt‐60 data. Conclusions: We demonstrate the use of a unique functional argument to linearize the inherently non‐linear response of a radiochromic Film based reference Dosimetry system. In this way, relative Dosimetry can be conveniently performed using radiochromic Film Dosimetry system without the need of establishing an absolute calibration curve. One author is from GAFCHROMICTM Films manufacturer
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Reference radiochromic Film Dosimetry in kilovoltage photon beams during CBCT image acquisition.
Medical physics, 2010Co-Authors: Nada Tomic, Slobodan Devic, François Deblois, Jan SeuntjensAbstract:Purpose: A common approach for dose assessment during cone beam computed tomography(CBCT) acquisition is to use thermoluminescent detectors for skindose measurements (on patients or phantoms) or ionization chamber (in phantoms) for body dose measurements. However, the benefits of a daily CBCTimage acquisition such as margin reduction in planning target volume and the image quality must be weighted against the extra dose received during CBCT acquisitions. Methods: The authors describe a two-dimensional reference Dosimetry technique for measuring dose from CBCT scans using the on-board imaging system on a Varian Clinac-iX linear accelerator that employs the XR-QA radiochromic Film model, specifically designed for dose measurements at low energy photons. The CBCTdose measurements were performed for three different body regions (head and neck, pelvis, and thorax) using humanoid Rando phantom. Results: The authors report on both surface dose and dose profiles measurements during clinical CBCT procedures carried out on a humanoid Rando phantom. Our measurements show that the surface doses per CBCT scan can range anywhere between 0.1 and 4.7 cGy, with the lowest surface dose observed in the head and neck region, while the highest surface dose was observed for the Pelvis spot light CBCT protocol in the pelvic region, on the posterior side of the Rando phantom. The authors also present results of the uncertainty analysis of our XR-QA radiochromic Film Dosimetry system. Conclusions: Radiochromic Film Dosimetry protocol described in this work was used to perform dose measurements during CBCT acquisitions with the one-sigma dose measurement uncertainty of up to 3% for doses above 1 cGy. Our protocol is based on Film exposure calibration in terms of “air kerma in air,” which simplifies both the calibration procedure and reference Dosimetry measurements. The results from a full Monte Carlo investigation of the dose conversion of measured XR-QA Film dose at the surface into dose to water (or water kerma) at the surface of the phantom indicate that, for typical beam qualities used in CBCT, this conversion can be approximated by simple mass-energy absorption coefficient ratios water-to-air.
Nada Tomic - One of the best experts on this subject based on the ideXlab platform.
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Reference radiochromic Film Dosimetry: Review of technical aspects
Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Associ, 2016Co-Authors: Slobodan Devic, Nada Tomic, David LewisAbstract:For decades, Film was used as a powerful two-dimensional (2D) Dosimetry tool for radiotherapy treatment verification and quality assurance. Unlike the old silver-halide based radiographic Films, radiochromic Films change its color upon irradiation without the need for chemical development. Radiation dose deposited within a sensitive layer of the radiochromic Film initiates polymerization of the active component, the degree of which depends on the amount of energy deposited. Response of the Film to radiation is commonly expressed in terms of optical density change, which can be easily measured by any photometric device. However, a number of factors may have an impact on the signal detected by the measuring device. This review summarizes technical aspects associated with the establishment of reference radiochromic Film Dosimetry and its subsequent use for either clinical or research applications.
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Linearization of dose-response curve of the radiochromic Film Dosimetry system.
Medical physics, 2012Co-Authors: Slobodan Devic, Nada Tomic, Saad Aldelaijan, François Deblois, Jan Seuntjens, Maria F. Chan, Dave LewisAbstract:Purpose: Despite numerous advantages of radiochromic Film dosimeter (high spatial resolution, near tissue equivalence, low energy dependence) to measure a relative dose distribution with Film, one needs to first measure an absolute dose (following previously established reference Dosimetry protocol) and then convert measured absolute dose values into relative doses. In this work, we present result of our efforts to obtain a functional form that would linearize the inherently nonlinear dose–response curve of the radiochromic Film Dosimetry system. Methods: Functional form [ ζ = (−1)·netOD(2/3)/ln(netOD)] was derived from calibration curves of various previously established radiochromic Film Dosimetry systems. In order to test the invariance of the proposed functional form with respect to the Film model used we tested it with three different GAFCHROMIC™ Film models (EBT, EBT2, and EBT3) irradiated to various doses and scanned on a same scanner. For one of the Film models (EBT2), we tested the invariance of the functional form to the scanner model used by scanning irradiated Film pieces with three different flatbed scanner models (Epson V700, 1680, and 10000XL). To test our hypothesis that the proposed functional argument linearizes the response of the radiochromic Film Dosimetry system, verification tests have been performed in clinical applications: percent depth dose measurements, IMRT quality assurance (QA), and brachytherapy QA. Results: Obtained R2 values indicate that the choice of the functional form of the new argument appropriately linearizes the dose response of the radiochromic Film Dosimetry system we used. The linear behavior was insensitive to both Film model and flatbed scanner model used. Measured PDD values using the green channel response of the GAFCHROMIC™ EBT3 Film model are well within ±2% window of the local relative dose value when compared to the tabulated Cobalt-60 data. It was also found that criteria of 3%/3 mm for an IMRT QA plan and 3%/2 mm for a brachytherapy QA plan are passing 95% gamma function points. Conclusions: In this paper, we demonstrate the use of functional argument to linearize the inherently nonlinear response of a radiochromic Film based reference Dosimetry system. In this way, relative Dosimetry can be conveniently performed using radiochromic Film Dosimetry system without the need of establishing calibration curve.
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TH‐E‐BRB‐02: Linearization of Dose Response Curve for the Radiochromic Film Dosimetry System
Medical Physics, 2012Co-Authors: Dave Lewis, Slobodan Devic, Nada Tomic, Saad Aldelaijan, François Deblois, Maria F. Chan, Jan SeuntjensAbstract:Purpose: In order to measure relative dose distribution with radiochromic Film, one need to first measure an absolute dose (following previously established reference Dosimetry protocol) and then convert measured absolute dose into relative dose. We present here result of our efforts to establish a functional form that converts the inherently non‐linear dose response curve of the radiochromic Film Dosimetry system into liner one. Methods: In order to test the invariance of the proposed functional form with respect to the Film or scanner model used, we have tested it on Film pieces from three different GAFCHROMICTM Film models (EBT, EBT‐2, and EBT‐3) irradiated to various doses and scanned on a single scanner. for one of the Film models we have also tested it by scanning with three different flatbed scanner models (Epson V700, 1680, and 10000XL). To test our hypothesis that the proposed functional argument linearizes the response of the radiochromic Film Dosimetry system, we performed a measurement of percent depth dose (PDD) curves in Cobalt‐60 beam. Results: Obtained R2 values indicate that the choice of the functional form of the new argument (ζ) appropriately linearizes the dose response of the radiochromic Film Dosimetry system we used. The linear behavior was insensitive to both Film model and flatbed scanner model used. Measured PDD values using the green channel response of the GAFCHROMICTM EBT‐3 Film model are well within ±2% window of the local relative dose value when compared to the tabulated Cobalt‐60 data. Conclusions: We demonstrate the use of a unique functional argument to linearize the inherently non‐linear response of a radiochromic Film based reference Dosimetry system. In this way, relative Dosimetry can be conveniently performed using radiochromic Film Dosimetry system without the need of establishing an absolute calibration curve. One author is from GAFCHROMICTM Films manufacturer
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Reference radiochromic Film Dosimetry in kilovoltage photon beams during CBCT image acquisition.
Medical physics, 2010Co-Authors: Nada Tomic, Slobodan Devic, François Deblois, Jan SeuntjensAbstract:Purpose: A common approach for dose assessment during cone beam computed tomography(CBCT) acquisition is to use thermoluminescent detectors for skindose measurements (on patients or phantoms) or ionization chamber (in phantoms) for body dose measurements. However, the benefits of a daily CBCTimage acquisition such as margin reduction in planning target volume and the image quality must be weighted against the extra dose received during CBCT acquisitions. Methods: The authors describe a two-dimensional reference Dosimetry technique for measuring dose from CBCT scans using the on-board imaging system on a Varian Clinac-iX linear accelerator that employs the XR-QA radiochromic Film model, specifically designed for dose measurements at low energy photons. The CBCTdose measurements were performed for three different body regions (head and neck, pelvis, and thorax) using humanoid Rando phantom. Results: The authors report on both surface dose and dose profiles measurements during clinical CBCT procedures carried out on a humanoid Rando phantom. Our measurements show that the surface doses per CBCT scan can range anywhere between 0.1 and 4.7 cGy, with the lowest surface dose observed in the head and neck region, while the highest surface dose was observed for the Pelvis spot light CBCT protocol in the pelvic region, on the posterior side of the Rando phantom. The authors also present results of the uncertainty analysis of our XR-QA radiochromic Film Dosimetry system. Conclusions: Radiochromic Film Dosimetry protocol described in this work was used to perform dose measurements during CBCT acquisitions with the one-sigma dose measurement uncertainty of up to 3% for doses above 1 cGy. Our protocol is based on Film exposure calibration in terms of “air kerma in air,” which simplifies both the calibration procedure and reference Dosimetry measurements. The results from a full Monte Carlo investigation of the dose conversion of measured XR-QA Film dose at the surface into dose to water (or water kerma) at the surface of the phantom indicate that, for typical beam qualities used in CBCT, this conversion can be approximated by simple mass-energy absorption coefficient ratios water-to-air.
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Sensitivity of linear CCD array based Film scanners used for Film Dosimetry.
Medical physics, 2006Co-Authors: Slobodan Devic, Yi Zhen Wang, Nada Tomic, Ervin B PodgorsakAbstract:Film Dosimetry is commonly performed by using linear CCD array transmission optical densitometers. However, these devices suffer from a variation in response along the detector array. If not properly corrected for, this nonuniformity may lead to significant overestimations of the measured dose as one approaches regions close to the edges of the scanning region. In this note, we present measurements of the spatial response of an AGFA Arcus II document scanner used for radiochromic Film Dosimetry. Results and methods presented in this work can be generalized to other CCD based transmission scanners used for Film Dosimetry employing either radiochromic or radiographic Films.
Ignasi Mendez - One of the best experts on this subject based on the ideXlab platform.
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Radiochromic Film Dosimetry: protocol and model selection
2018Co-Authors: Ignasi MendezAbstract:This thesis aimed to improve the accuracy of radiochromic Film Dosimetry with a main focus on optimizing protocols and Dosimetry models. The research was divided in four publications. The first paper [Mendez I, Hartman V, Hudej R, Strojnik A, and Casar B, "Gafchromic EBT2 Film Dosimetry in reflection mode with a novel plan-based calibration method", Med. Phys. 40, 011720 (2013)] studied Film Dosimetry with a flatbed scanner in reflection mode, proposed a new plan-based calibration method, and selected models for sensitometric curves and lateral corrections. In the second paper [Mendez I, Peterlin P, Hudej R, Strojnik A, and Casar B, "On multichannel Film Dosimetry with channel-independent perturbations", Med. Phys. 41, 011705 (2014)], different channel-independent perturbation models for radiochromic Film Dosimetry were analysed and compared, explaining their implicit assumptions and inherent uncertainties. Several elements of the Dosimetry protocol were compared as well. The third article [Mendez I, "Model selection for radiochromic Film Dosimetry", Phys. Med. Biol. 60, 4089 (2015)] deepened the selection of the Dosimetry protocol by examining whether lateral corrections, scanning prior to the irradiation, and multichannel methods significantly improved the accuracy and precision of Film doses. Also, a general perturbation model was proposed in this article. Finally, the fourth publication [Mendez I, Sljivic Ž, Hudej R, Jenko A, and Casar B. "Grid patterns, spatial inter-scan variations and scanning reading repeatability in radiochromic Film Dosimetry", Physica Medica (2016)] studied several sources of uncertainty related to the repeatability of flatbed scanners. Grid patterns and positioning inaccuracies were discovered, and a new method to correct inter-scan variations was proposed.
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[OA155] Big data in radiochromic Film Dosimetry
Physica Medica, 2018Co-Authors: Ignasi Mendez, Bozidar CasarAbstract:Purpose Radiochromic.com is a web application for radiochromic Film Dosimetry. Hundreds of users of the application worldwide upload and process Film images in the cloud. Once anonymized, these Film images, along with sensitometric curves, lateral corrections, etc, form a large sample of data with an enormous potential as a research tool for improving radiochromic Film Dosimetry. For instance, the development of universal/generic sensitometric curves and lateral corrections, the detection of mistakes made during Film measurements, the optimization of Dosimetry protocols, the reduction of uncertainties, etc, may be feasible. A comprehensive analysis of the data is a long term project. In this work, the first steps were taken. Methods The sample consisted of 8190 different Film images (more than 20 Gb) uploaded by 277 users, as well as 993 calibrations and 748 lateral corrections. A descriptive statistical analysis of the sample was performed. The feasibility of generic lateral corrections was investigated. Results The descriptive analysis of the data offers an approximate picture of the most common Dosimetry systems and protocols employed in Film Dosimetry. Film model, lot, scanner, resolution, dimensions of the scanning area, or post irradiation time were available. As an example, the most common scanner type in the sample was Epson Expression 10000XL-12000XL, with 63% of the users, followed by Epson Perfection V700-V850 scanners with 20%. Generic lateral corrections calculated according to the Absolute correction method proposed by Mendez [Ref:I. Mendez, “Model selection for radiochromic Film Dosimetry,” Phys. Med. Biol. 60, 4089 (2015)] were found for Epson Expression 10000XL-12000XL and Epson Perfection V700-V850 scanners. At this stage of the research, the generic lateral corrections are considered as gold standards. They are not intended to release from the need of measuring lateral corrections, but to reduce the uncertainty derived from not applying lateral corrections whenever measuring them is not possible. Conclusions A large sample of radiochromic Film Dosimetry data from hundreds of users worldwide opens up new research areas with many potential applications. In this work, the sample and the first results were presented.
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model selection for radiochromic Film Dosimetry
arXiv: Medical Physics, 2015Co-Authors: Ignasi MendezAbstract:The purpose of this study was to find the most accurate model for radiochromic Film Dosimetry by comparing different channel independent perturbation models. A model selection approach based on (algorithmic) information theory was followed, and the results were validated using gamma-index analysis on a set of benchmark test cases. Several questions were addressed: (a) whether incorporating the information of the non-irradiated Film, by scanning prior to irradiation, improves the results; (b) whether lateral corrections are necessary when using multichannel models; (c) whether multichannel Dosimetry produces better results than single-channel Dosimetry; (d) which multichannel perturbation model provides more accurate Film doses. It was found that scanning prior to irradiation and applying lateral corrections improved the accuracy of the results. For some perturbation models, increasing the number of color channels did not result in more accurate Film doses. Employing Truncated Normal perturbations was found to provide better results than using Micke-Mayer perturbation models.} Among the models being compared, the triple-channel model with Truncated Normal perturbations, net optical density as the response and subject to the application of lateral corrections was found to be the most accurate model. The scope of this study was circumscribed by the limits under which the models were tested. In this study, the Films were irradiated with megavoltage radiotherapy beams, with doses from about 20 cGy to 600 cGy, entire (8 ${\rm inch}$ $\times$ 10 ${\rm inch}$) Films were scanned, the functional form of the sensitometric curves was a polynomial and the different lots were calibrated using the plane-based method.
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Model selection for radiochromic Film Dosimetry.
Physics in medicine and biology, 2015Co-Authors: Ignasi MendezAbstract:The purpose of this study was to find the most accurate model for radiochromic Film Dosimetry by comparing different channel independent perturbation models. A model selection approach based on (algorithmic) information theory was followed, and the results were validated using gamma-index analysis on a set of benchmark test cases. Several questions were addressed: (a) whether incorporating the information of the non-irradiated Film, by scanning prior to irradiation, improves the results; (b) whether lateral corrections are necessary when using multichannel models; (c) whether multichannel Dosimetry produces better results than single-channel Dosimetry; (d) which multichannel perturbation model provides more accurate Film doses. It was found that scanning prior to irradiation and applying lateral corrections improved the accuracy of the results. For some perturbation models, increasing the number of color channels did not result in more accurate Film doses. Employing Truncated Normal perturbations was found to provide better results than using Micke–Mayer perturbation models. Among the models being compared, the triple-channel model with Truncated Normal perturbations, net optical density as the response and subject to the application of lateral corrections was found to be the most accurate model. The scope of this study was circumscribed by the limits under which the models were tested. In this study, the Films were irradiated with megavoltage radiotherapy beams, with doses from about 20–600 cGy, entire (8 inch × 10 inch) Films were scanned, the functional form of the sensitometric curves was a polynomial and the different lots were calibrated using the plane-based method.
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on multichannel Film Dosimetry with channel independent perturbations
Medical Physics, 2013Co-Authors: Ignasi Mendez, Primož Peterlin, R Hudej, A Strojnik, Bozidar CasarAbstract:Purpose: Different multichannel methods for Film Dosimetry have been proposed in the literature. Two of them are the weighted mean method and the method put forth byMicke et al. [“Multichannel Film Dosimetry with nonuniformity correction,” Med. Phys. 38, 2523–2534 (2011)] and Mayer et al. [“Enhanced Dosimetry procedures and assessment for EBT2 radiochromic Film,” Med. Phys. 39, 2147–2155 (2012)]. The purpose of this work was to compare their results and to develop a generalized channel-independent perturbations framework in which both methods enter as special cases. Methods: Four models of channel-independent perturbations were compared: weighted mean, Micke–Mayer method, uniform distribution, and truncated normal distribution. A closed-form formula to calculate Film doses and the associated type B uncertainty for all four models was deduced. To evaluate the models, Film dose distributions were compared with planned and measured dose distributions. At the same time, several elements of the Dosimetry process were compared: Film type EBT2 versus EBT3, different waiting-time windows, reflection mode versus transmission mode scanning, and planned versus measured dose distribution for Film calibration and for γ-index analysis. The methods and the models described in this study are publicly accessible through IRISEU. Alpha 1.1 ( http://www.iriseu.com ). IRISEU. is a cloud computing webmore » application for calibration and Dosimetry of radiochromic Films. Results: The truncated normal distribution model provided the best agreement between Film and reference doses, both for calibration and γ-index verification, and proved itself superior to both the weighted mean model, which neglects correlations between the channels, and the Micke–Mayer model, whose accuracy depends on the properties of the sensitometric curves. With respect to the selection of Dosimetry protocol, no significant differences were found between transmission and reflection mode scanning, between 75 ± 5 min and 20 ± 1 h waiting-time windows or between employing EBT2 or EBT3 Films. Significantly better results were obtained when a measured dose distribution was used instead of a planned one as reference for the calibration, and when a planned dose distribution was used instead of a measured one as evaluation for the γ-analysis. Conclusions: The truncated normal distribution model of channel-independent perturbations was found superior to the other three models under comparison and the authors propose its use for multichannel Dosimetry.« less