Preliminary Investigation of X-ray Imaging for Dose Extraction of BANG® Polymer Gel in Intensity Modulated Radiation Therapy PDF Download
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Author: Chhipo Sath
Publisher:
ISBN:
Category : Polymer colloids
Languages : en
Pages : 242
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Book Description
This study investigated gel dosimetry with X-ray CT imaging as a possible means for extracting dose information from a 3D gel dosimeter. Currently Optical CT and MRI are the popular means of dose extraction, but X-ray CT imaging has the advantage of being more convenient and cost effective. The dosimetric system was based on the BANG® polymer gel (MGS Research) and an ordinary clinical X-ray CT unit. The gel system was analyzed for its effectiveness in detecting absorbed dose from a 10 MV Linac unit. This study investigated calibration doses up to 8 Gy and two fractions of an IMRT treatment plan for a total dose of 4.22 Gy. The irradiation plans were generated by the Varian Eclipse® treatment planning system and delivered at OHSU. One week post irradiations the BANG® polymer gels were analyzed using X-ray CT imaging at OHSU. The imaging parameters were unique to this investigation. Post irradiation the BANG® gel dosimeter responded to the absorbed doses through the process known as polymerization. The BANG® polymer gel dosimeter changed chemically and physically. A density change occurring in the location of irradiation allowed for detection via X-ray Imaging. A tube potential of 120 kV was selected for better signal to noise ratio and thin image slices of 1 mm was used for greater spatial resolution. The use of X-ray imaging with these specific imaging parameters proved to be convenient and effective. Images of the gel which received no radiation were studied to build a background evaluation. Post irradiation images were evaluated for dose response. This study showed that X-ray imaging was able to detect the change within the gel due to irradiation with a response of about 0.66 ± 0.03 pixel values per Gy. The BANG® gel dosimeter was characterized for its response to radiation, dose sensitivity, dose resolution, and dose distribution. We found our system to have a high dose sensitivity of 0.96 ± 0.6 H/Gy. The X-ray CT images were able to differentiate between doses with a resolution of 39% within the mean dose. From these finding we were able to build dose distributions and dose maps for our calibration and treatment phantoms. The conclusion of this preliminary investigation found X-ray CT imaging to be successful for dose extraction purposes. We note that there are still areas in gel dosimetry which need additional research such as development in software or code to integrate, analyze the dose response, and compare the results with predicted dose distribution generated by the treatment plans. Using X-ray CT will certainly decrease the cost of the 3D Gel dosimetry systems and with increased clinical use 3D gel dosimetry will soon allow for better quality assurance of radiotherapy treatments.
Author: Chhipo Sath
Publisher:
ISBN:
Category : Polymer colloids
Languages : en
Pages : 242
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Book Description
This study investigated gel dosimetry with X-ray CT imaging as a possible means for extracting dose information from a 3D gel dosimeter. Currently Optical CT and MRI are the popular means of dose extraction, but X-ray CT imaging has the advantage of being more convenient and cost effective. The dosimetric system was based on the BANG® polymer gel (MGS Research) and an ordinary clinical X-ray CT unit. The gel system was analyzed for its effectiveness in detecting absorbed dose from a 10 MV Linac unit. This study investigated calibration doses up to 8 Gy and two fractions of an IMRT treatment plan for a total dose of 4.22 Gy. The irradiation plans were generated by the Varian Eclipse® treatment planning system and delivered at OHSU. One week post irradiations the BANG® polymer gels were analyzed using X-ray CT imaging at OHSU. The imaging parameters were unique to this investigation. Post irradiation the BANG® gel dosimeter responded to the absorbed doses through the process known as polymerization. The BANG® polymer gel dosimeter changed chemically and physically. A density change occurring in the location of irradiation allowed for detection via X-ray Imaging. A tube potential of 120 kV was selected for better signal to noise ratio and thin image slices of 1 mm was used for greater spatial resolution. The use of X-ray imaging with these specific imaging parameters proved to be convenient and effective. Images of the gel which received no radiation were studied to build a background evaluation. Post irradiation images were evaluated for dose response. This study showed that X-ray imaging was able to detect the change within the gel due to irradiation with a response of about 0.66 ± 0.03 pixel values per Gy. The BANG® gel dosimeter was characterized for its response to radiation, dose sensitivity, dose resolution, and dose distribution. We found our system to have a high dose sensitivity of 0.96 ± 0.6 H/Gy. The X-ray CT images were able to differentiate between doses with a resolution of 39% within the mean dose. From these finding we were able to build dose distributions and dose maps for our calibration and treatment phantoms. The conclusion of this preliminary investigation found X-ray CT imaging to be successful for dose extraction purposes. We note that there are still areas in gel dosimetry which need additional research such as development in software or code to integrate, analyze the dose response, and compare the results with predicted dose distribution generated by the treatment plans. Using X-ray CT will certainly decrease the cost of the 3D Gel dosimetry systems and with increased clinical use 3D gel dosimetry will soon allow for better quality assurance of radiotherapy treatments.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Polymer gel dosimetry, in conjunction with x-ray computed tomography (x-ray CT) imaging, is a three-dimensional dosimetric tool that shows promise in the verification of complex radiation therapy treatments. Previous studies have shown that x-ray CT imaging of gel dosimeters is robust, easy-to-use, and has wide clinical accessibility. The effects of x-ray CT dose imparted to the gel dosimeter, during imaging of the delivered therapy dose distributions, is not well understood. This thesis quantifies the effects of CT dose on normoxic polyacrylamide gel (nPAG) dosimeters. The investigation is comprised of four parts. First, quantification of the x-ray CT dose given during CT imaging of nPAG gels was measured using ion chamber measurements and filmed dose profiles for a range of typical gel dosimetry imaging protocols (200 mAs (current-time), 120-140 kVp (peak potential energy of photons), 2-10 mm slice thickness). It was found that CT doses ranged from 0.007 Gy/slice (120 kVp, 2 mm) to 0.021 Gy/slice (140 kVp, 10 mm) for volumetric phantoms. Second, Raman spectroscopy was used to determine the effect of photon energy on the dose response of nPAG dosimeters exposed to photon energies from a CT scanner (140 kVp photons) and from a Linac (6 MV photons). A weaker response was exhibited within the gels irradiated with kV photons than MV photons. Thirdly, the measurements of the given x-ray CT dose as established in the first study and the dose response of the polymer gel to different photon energies in the second study were correlated to estimate the induced changes of the nPAG CT number ("NCT), caused by x-ray CT imaging of the polymer gel. (CT number is defined to be the measured attenuation coefficient normalized to water.) For typical gel imaging protocols (as above with 16-32 image averages), it was found that "NCT
Author: Ben Mijnheer
Publisher: CRC Press
ISBN: 1482252228
Category : Science
Languages : en
Pages : 696
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Book Description
Provides a complete overview of the principles, hardware, measurement methods, and clinical applications of three-dimensional dosimetry. Explains basic concepts with emphasis on 3D dose measurements and validation of 3D dose calculations as a key application of 3D dosimetry. Discusses accuracy requirements for 3D dosimetry in advanced radiotherapy as well as important topics such as audits, quality assurance, and testing. Presents state of the art detector and point detector instruments and systems, gel dosimetry, and electronic portal imaging device dosimetry. Addresses the main measurement approaches, from small-field dosimetry to 4D dosimetry, Monte Carlo techniques, and methods for quantifying differences in 3D dose distributions.
Author: Patricia Baxter
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Polymer gel dosimetry, in conjunction with x-ray computed tomography (x-rayCT) imaging, is a three-dimensional dosimetric tool that shows promise in the verificationof complex radiation therapy treatments. Previous studies have shown thatx-ray CT imaging of gel dosimeters is robust, easy-to-use, and has wide clinical accessibility. The effects of x-ray CT dose imparted to the gel dosimeter, during imaging ofthe delivered therapy dose distributions, is not well understood. This thesis quantifiesthe effects of CT dose on normoxic polyacrylamide gel (nPAG) dosimeters. The investigation is comprised of four parts. First, quantification of the x-rayCT dose given during CT imaging of nPAG gels was measured using ion chambermeasurements and filmed dose profiles for a range of typical gel dosimetry imagingprotocols (200 mAs (current-time), 120-140 kVp (peak potential energy of photons),2-10 mm slice thickness). It was found that CT doses ranged from 0.007 Gy/slice (120kVp, 2 mm) to 0.021 Gy/slice (140 kVp, 10 mm) for volumetric phantoms. Second, Raman spectroscopy was used to determine the effect of photon energy on the doseresponse of nPAG dosimeters exposed to photon energies from a CT scanner (140 kVp photons) and from a Linac (6 MV photons). A weaker response was exhibited withinthe gels irradiated with kV photons than MV photons. Thirdly, the measurementsof the given x-ray CT dose as established in the first study and the dose response ofthe polymer gel to different photon energies in the second study were correlated toestimate the induced changes of the nPAG CT number ("NCT), caused by x-ray CTimaging of the polymer gel. (CT number is defined to be the measured attenuationcoefficient normalized to water.) For typical gel imaging protocols (as above with16-32 image averages), it was found that "NCT 0.2 H is induced in active nPAGgel dosimeters. This "NCT is below the current threshold of detectability of CTnPAG gel dosimetry. Finally, the traditional method of chemically fixing the doseresponse mechanism of nPAG gels by passive oxygenation of the gel, is investigatedto determine if oxygenation would mitigate the changes caused by x-ray CT imaging of the gels. It was determined that oxygen diffusion was too slow to cause fixationof nPAG dosimeters, as the diffusion constant was 1.2? 0.2? 10?6cm2/s, or 25% ofthe diffusion constant for anoxic PAG gel dosimeters. In conclusion, it was found that x-ray CT dose in polymer gel dosimeters is nota concern for standard gel imaging protocols. X-ray CT dose can potentially be aconcern when large numbers of image averages (e.g.60 image averages) are utilized, as in gel imaging protocols for high-resolution scans.
Author: Holly A. Johnston
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
X-ray computed tomography (CT) polymer gel dosimetry (PGD) is an attractive tool for three-dimensional (3D) radiation therapy (RT) treatment verification due to the availability of CT scanners in RT clinics. Nevertheless, wide-spread use of the technique has been hindered by low signal-to-noise CT images largely resulting from gel formulations with low radiation sensitivity. However, a new gel recipe with enhanced dose sensitivity was recently introduced that shows great promise for use with CT readout. This dissertation describes development of an CT PGD system for 3D verification of RT treatments using the new gel formulation. The work is divided into three studies: gel characterization, commissioning of a multislice CT scanner and investigation of a dose rate dependence observed during gel characterization.The first component of this work examines the dosimetric properties of the new gel formulation. The response of the gel is found to be stable between 15 - 36 hours post-irradiation and excellent batch reproducibility is seen for doses between 0 - 28 Gy. A dose rate dependence is found for gels irradiated between 100 - 600 MU/min, indicating machine dose rate must be consistent for calibration and test irradiations to avoid dosimetric error. An example clinical application is also presented using an IMRT treatment verification that demonstrates the potential of the system for use in modern RT. The second component of this work focuses on commissioning a multislice CT scanner for CT PGD. A new slice-by-slice background subtraction technique is introduced to account for the anode heel effect. Additional investigations show recommendations for optimizing image quality in CT PGD using a single slice machine also apply to multislice scanners. In addition, the consistency of CT numbers across the multislice detector array is found to be excellent for all slice thicknesses. Further work is performed to assess the tube load characteristics of the scanner and develop a scanning protocol for imaging large gel volumes. Finally, images acquired throughout the volume of an unirradiated active gel show variations in CT data across each image on the order of 7 HU. However, these variations are not expected to greatly influence gel measurements as they are consistent throughout the gel volume. The third component of this work examines the dose rate dependence found during gel characterization. Studies using gel vials and 1 L cylinders indicate the response of the gel does not depend on changes in mean dose rate on the order of seconds to minutes. However, the machine dose rate remains, indicating variations in dose rate on the order of milliseconds influence the response of the gel. An attempt is made to mitigate the effect by increasing the concentration of antioxidant in the gel system but results in reduced overall response. Further work is performed to determine if self-crosslinking of one of the gel components contributes to the observed machine dose rate dependence.In summary, this dissertation has significantly advanced the field of gel dosimetry by providing a prototype CT PGD system with enhanced dose resolution for complex RT treatment verification.
Author:
Publisher:
ISBN:
Category : Medicine
Languages : en
Pages : 2002
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Book Description
Vols. for 1963- include as pt. 2 of the Jan. issue: Medical subject headings.
Author: International Atomic Energy Agency
Publisher: IAEA
ISBN:
Category : Business & Economics
Languages : en
Pages : 704
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Book Description
This publication is aimed at students and teachers involved in teaching programmes in field of medical radiation physics, and it covers the basic medical physics knowledge required in the form of a syllabus for modern radiation oncology. The information will be useful to those preparing for professional certification exams in radiation oncology, medical physics, dosimetry or radiotherapy technology.
Author: Sven Å. J. Bäck
Publisher:
ISBN:
Category : Magnetic resonance imaging
Languages : en
Pages : 192
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Book Description
Author: John William Tranter Spinks
Publisher: Wiley-Interscience
ISBN:
Category : Science
Languages : en
Pages : 600
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Book Description
This text on radiation chemistry covers a number of topics, including the development of radiation chemistry, sources of high-energy radiation, dosimetry, organic materials and solids and the applications of high-energy radiation in chemical synthesis and in commercial processes.
Author: Karupppasamy Subburaj
Publisher: BoD – Books on Demand
ISBN: 9533079436
Category : Medical
Languages : en
Pages : 362
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Book Description
Since its introduction in 1972, X-ray computed tomography (CT) has evolved into an essential diagnostic imaging tool for a continually increasing variety of clinical applications. The goal of this book was not simply to summarize currently available CT imaging techniques but also to provide clinical perspectives, advances in hybrid technologies, new applications other than medicine and an outlook on future developments. Major experts in this growing field contributed to this book, which is geared to radiologists, orthopedic surgeons, engineers, and clinical and basic researchers. We believe that CT scanning is an effective and essential tools in treatment planning, basic understanding of physiology, and and tackling the ever-increasing challenge of diagnosis in our society.
