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Clair Baldock - One of the best experts on this subject based on the ideXlab platform.
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high resolution Gel dosimetry of a hdr brachytherapy source using normoxic Polymer Gel dosimeters preliminary study
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2006Co-Authors: C Hurley, C Mclucas, Giovanni Pedrazzini, Clair BaldockAbstract:Polymer Gel dosimetry has been shown to be an effective tool in the analysis of radiotherapy treatments in cancer therapy, being used to map the dose distribution around an irradiation pattern of a Polymer Gel dosimeter. Combined with high-resolution magnetic resonance imaging (MRI), Polymer Gel dosimetry can be an effective dosimetry tool to map dose distributions with high spatial resolution (∼100 μm). Previously polyacrylamide Polymer Gel dosimetry required a strict hypoxic environment to protect the Gel from oxygen infiltration as oxygen inhibits the Polymerization reaction used to correlate to absorbed dose. However, with the advent of normoxic Polymer Gels, a strict hypoxic environment is not required. Normoxic Polymer Gel dosimeters can be manufactured under normal atmospheric conditions. This study assessed the use of a MAGIC normoxic Polymer Gel dosimeter to accurately map the dose distribution of a single-line irradiation and a point source irradiation from a brachytherapy radiation source administered through a nylon catheter inserted into the Gel dosimeter. The phantoms were irradiated to a dose of 10 Gy at 2 mm from the source center and imaged using high-resolution MRI with an in-plane pixel size of 0.1055 mm/pixel. Good agreement was found between the dose points predicted by the computer treatment-planning system and the measured normalized dose profiles in the Gel dosimeter. The use of normoxic Polymer Gel dosimeters with high-resolution MRI evaluation shows promise as an effective tool in applications requiring accurate dose distributions in high resolution, such as intravascular brachytherapy.
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a preliminary study of the novel application of normoxic Polymer Gel dosimeters for the measurement of ctdi on diagnostic x ray ct scanners
Medical Physics, 2005Co-Authors: Brendan Hill, A J Venning, Clair BaldockAbstract:Computer tomography dose index (CTDI) is a measurement undertaken during acceptance testing and subsequent quality assurance measurements of diagnostic x-ray CT scanners for the determination of patient dose. Normoxic Polymer Gel dosimeters have been used for the first time to measure dose and subsequently CTDI during acceptance testing of a CT scanner and compared with the conventional ionization chamber measurement for a range of imaging protocols. The normoxic Polymer Gel dosimeter was additionally used to simultaneously determine slice-width dose profiles and CTDI in the transaxial plane, the measurements of which are usually determined with thermoluminescent dosimetry or film. The resulting CTDI for all slice widths calculated from the normoxic Polymer Gel dosimeter were within corresponding ionization chamber CTDI values. Slice-width dose-profiles full-width half-maximum values from the normoxic Polymer Gel dosimeter were compared to the slice sensitivity profiles and were within the tolerances of the manufacturer. Normoxic Polymer Gel dosimeters have been shown to be a useful device for determining CTDI and dose distributions for CT equipment, and provide additional information not possible with just the use of an ionization chamber.
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radiological properties of normoxic Polymer Gel dosimeters
Medical Physics, 2005Co-Authors: A J Venning, K Nitschke, P Keall, Clair BaldockAbstract:The radiological properties of the normoxic Polymer Gel dosimeters MAGIC, MAGAS, and MAGAT [methacrylic and ascorbic acid in Gelatin initiated by copper; methacrylic acid Gelatine Gel with ascorbic acid; and methacrylic acid Gelatine and tetrakis (hydroxymethyl) phosphonium chloride, respectively] have been investigated. The radiological water equivalence was determined by comparing the Polymer Gel macroscopic photon and electron interaction cross sections over the energy range from 10 keV to 20 MeV and by Monte Carlo modeling of depth doses. Normoxic Polymer Gel dosimeters have a high Gelatine and monomer concentration and therefore mass density (kg m{sup -3}) up to 3.8% higher than water. This results in differences between the cross-section ratios of the normoxic Polymer Gels and water of up to 3% for the attenuation, energy absorption, and collision stopping power coefficient ratios through the Compton dominant energy range. The mass cross-section ratios were within 2% of water except for the mass attenuation and energy absorption coefficients ratios, which showed differences with water of up to 6% for energies less than 100 keV. Monte Carlo modeling was undertaken for the Polymer Gel dosimeters to model the electron and photon transport resulting from a 6 MV photon beam. The absolute percentage differencesmore » between Gel and water were within 1% and the relative percentage differences were within 3.5%. The results show that the MAGAT Gel formulation is the most radiological water equivalent of the normoxic Polymer Gel dosimeters investigated due to its lower mass density measurement compared with MAGAS and MAGIC Gels.« less
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experimental study of attenuation properties of normoxic Polymer Gel dosimeters
Physics in Medicine and Biology, 2004Co-Authors: S Brindha, Brendan Hill, A J Venning, Clair BaldockAbstract:The change in linear attenuation coefficient with absorbed dose has been investigated for aqueous polyacrylamide, Gelatine and tetrakis (PAGAT) and aqueous methacrylic acid, Gelatine and tetrakis (MAGAT) normoxic Polymer Gel dosimeters using tetrakis (hydroxy methyl) phosphonium chloride as the antioxidant. The measured linear attenuation coefficient increased linearly with absorbed dose up to 15 Gy for PAGAT Gels and 10 Gy for MAGAT Gels. Computerized tomography (CT) numbers or Hounsfield units (H) were calculated from the linear attenuation coefficients and compared with values obtained using a CT scanner. Both calculated and measured CT numbers followed a similar pattern when fitted with a biexponential curve. The CT numbers obtained from linear attenuation measurements were found to be greater than that obtained with the CT scanner for both PAGAT and MAGAT Polymer Gels. The H-dose sensitivities of the MAGAT and PAGAT Polymer Gel dosimeters measured on a CT scanner were calculated to be (0.85 ± 0.08) H Gy−1 and (0.31 ± 0.03) H Gy−1, respectively. The H-dose sensitivities of the MAGAT and PAGAT Polymer Gel dosimeters from attenuation measurements were found to be (1.10 ± 0.66) H Gy−1 and (0.34 ± 0.01) H Gy−1, respectively.
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measurement of ultrasonic attenuation coefficient in Polymer Gel dosimeters
Physics in Medicine and Biology, 2003Co-Authors: Melissa L Mather, Paul Charles, Clair BaldockAbstract:A technique is described for investigation of the ultrasonic attenuation coefficient for evaluation of absorbed dose in Polymer Gel dosimeters. Using this technique the attenuation coefficient as a function of absorbed dose in PAG and MAGIC Polymer Gel dosimeters was measured. The ultrasonic attenuation coefficient dose sensitivity for PAG was found to be 2.9 ± 0.3 dB m−1 Gy−1 and for MAGIC Gel 4.2 ± 0.3 dB m−1 Gy−1. Unlike previous studies of ultrasonic attenuation in Polymer Gel dosimeters this technique enables a direct measure of the attenuation coefficient.
A J Venning - One of the best experts on this subject based on the ideXlab platform.
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Investigation of the MAGAS normoxic Polymer Gel dosimeter with Pyrex glass walls for clinical radiotherapy dosimetry
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2005Co-Authors: A J Venning, B. Healy, K. N. Nitschke, Clive BaldockAbstract:Abstract Depth doses for a 6 MV photon beam have been measured with the Methacrylic Acid Gelatin with AScorbic acid (MAGAS) Polymer Gel dosimeter contained in a cylindrical Pyrex glass phantom and Pyrex glass tubes and compared with depth doses calculated using Monte Carlo EGS4 code and ionisation chamber measurements in water. Differences between the Polymer Gel, Monte Carlo and ionisation chamber depth doses were up to 4%. Measurements were performed with an ionisation chamber under different thicknesses of Pyrex glass to determine correction factors for the Pyrex glass phantom wall material in the Polymer Gel measurement of depth dose. With radiological depth scaling and correction factors applied, the extent of agreement with ionisation chamber measurements in water was within 3%. The R 2 -dose response of the Polymer Gel in glass vials was linear up to 25 Gy. The MAGAS Polymer Gel dosimeter has shown potential as a clinical radiotherapy tool for the evaluation of depth dose. Further investigation is required to fully develop its capabilities and to reduce differences with measurements made with other dosimetry systems.
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investigation of the pagat Polymer Gel dosimeter using magnetic resonance imaging
Physics in Medicine and Biology, 2005Co-Authors: Brendan Hill, A J Venning, S Brindha, Brendan Healy, Clive BaldockAbstract:Investigation of the normoxic PAGAT Polymer Gel dosimeter has been undertaken. The concentrations of the chemical components of the Gel were varied and its response to ionizing radiation evaluated. Using MRI, the formulation to give the maximum change in the transverse relaxation rate R2 was determined to be 4.5% N, N'–methylene-bis-acrylamide (bis), 4.5% acrylamide (AA), 5% Gelatine, 5 mM tetrakis (hydroxymethyl) phosphonium chloride (THPC), 0.01 mM hydroquinone (HQ) and 86% H2O. The optimal post-manufacture irradiation and post-irradiation imaging times were both determined to be 12 h. The R2-dose response was linear up to 7 Gy with R2-dose sensitivities of (0.183 ± 0.005) s−1 Gy−1, (0.182 ± 0.005) s−1 Gy−1 and (0.192 ± 0.005) s−1 Gy−1 when imaged at 12 h, 7 days and 24 days post-irradiation, respectively. The R2-dose sensitivities were within the range of previously published values for the hypoxic PAG formulations. For the imaging parameters used in this study the optimum dose resolution was achieved for low doses. The normalized R2 edge response showed a high degree of spatial stability over a 24 day period. This study has shown that the normoxic PAGAT Polymer Gel has the properties of a dosimetric tool, which can be used in clinical radiotherapy. The PAGAT Polymer Gel has been shown to have similar qualities to the PAG Polymer Gel, while offering the significant advantage of simplification of the manufacturing procedure.
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the dose response of normoxic Polymer Gel dosimeters measured using x ray ct
British Journal of Radiology, 2005Co-Authors: Brendan Hill, A J Venning, C BaldockAbstract:X-ray CT was used to determine the dose response of normoxic Polymer Gel dosimeters. Normoxic Polymer Gel dosimeters were manufactured and irradiated up to 150 Gy. Up to 50 CT images were acquired on a Toshiba Aquilion Multislice CT scanner using protocols for 80 kV and 135 kV to determine dose response. HU-dose sensitivity, the linear regression of data for the HU versus dose for the linear part of the curve up to 60 Gy was 0.38±0.07 HU Gy−1 for 135 kV and 0.37±0.01 HU Gy−1 for 80 kV. Dose resolution was found to be < 1.3 Gy for an absorbed dose range up to 70 Gy for 135 kV, similar to that measured previously for polyacrylamide Gel (PAG). Although the HU-dose sensitivity was lower than that previously measured for PAG Gel dosimeters it had a greater range of absorbed dose indicating that normoxic Polymer Gel dosimeters have potential in CT Gel dosimetry.
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a preliminary study of the novel application of normoxic Polymer Gel dosimeters for the measurement of ctdi on diagnostic x ray ct scanners
Medical Physics, 2005Co-Authors: Brendan Hill, A J Venning, Clair BaldockAbstract:Computer tomography dose index (CTDI) is a measurement undertaken during acceptance testing and subsequent quality assurance measurements of diagnostic x-ray CT scanners for the determination of patient dose. Normoxic Polymer Gel dosimeters have been used for the first time to measure dose and subsequently CTDI during acceptance testing of a CT scanner and compared with the conventional ionization chamber measurement for a range of imaging protocols. The normoxic Polymer Gel dosimeter was additionally used to simultaneously determine slice-width dose profiles and CTDI in the transaxial plane, the measurements of which are usually determined with thermoluminescent dosimetry or film. The resulting CTDI for all slice widths calculated from the normoxic Polymer Gel dosimeter were within corresponding ionization chamber CTDI values. Slice-width dose-profiles full-width half-maximum values from the normoxic Polymer Gel dosimeter were compared to the slice sensitivity profiles and were within the tolerances of the manufacturer. Normoxic Polymer Gel dosimeters have been shown to be a useful device for determining CTDI and dose distributions for CT equipment, and provide additional information not possible with just the use of an ionization chamber.
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radiological properties of normoxic Polymer Gel dosimeters
Medical Physics, 2005Co-Authors: A J Venning, K Nitschke, P Keall, Clair BaldockAbstract:The radiological properties of the normoxic Polymer Gel dosimeters MAGIC, MAGAS, and MAGAT [methacrylic and ascorbic acid in Gelatin initiated by copper; methacrylic acid Gelatine Gel with ascorbic acid; and methacrylic acid Gelatine and tetrakis (hydroxymethyl) phosphonium chloride, respectively] have been investigated. The radiological water equivalence was determined by comparing the Polymer Gel macroscopic photon and electron interaction cross sections over the energy range from 10 keV to 20 MeV and by Monte Carlo modeling of depth doses. Normoxic Polymer Gel dosimeters have a high Gelatine and monomer concentration and therefore mass density (kg m{sup -3}) up to 3.8% higher than water. This results in differences between the cross-section ratios of the normoxic Polymer Gels and water of up to 3% for the attenuation, energy absorption, and collision stopping power coefficient ratios through the Compton dominant energy range. The mass cross-section ratios were within 2% of water except for the mass attenuation and energy absorption coefficients ratios, which showed differences with water of up to 6% for energies less than 100 keV. Monte Carlo modeling was undertaken for the Polymer Gel dosimeters to model the electron and photon transport resulting from a 6 MV photon beam. The absolute percentage differencesmore » between Gel and water were within 1% and the relative percentage differences were within 3.5%. The results show that the MAGAT Gel formulation is the most radiological water equivalent of the normoxic Polymer Gel dosimeters investigated due to its lower mass density measurement compared with MAGAS and MAGIC Gels.« less
Chuanfeng Chen - One of the best experts on this subject based on the ideXlab platform.
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supramolecular Polymer Gel with multi stimuli responsive self healing and erasable properties generated by host guest interactions
Polymer, 2013Co-Authors: Fei Zeng, Chuanfeng ChenAbstract:Abstract A supramolecular Polymer Gel formed between triptycene-based bis(crown ether) and coPolymer containing dibenzylammonium (DBA) moieties by host–guest interactions was described. We demonstrated the formation of the supramolecular Polymer networks between the bis(crown ether) and the coPolymer by the 1 H NMR spectroscopy and solution viscometry, and we also obtained a colorless and transparent supramolecular Polymer Gel at high concentration. Moreover, the supramolecular Polymer Gel showed multi-stimuli reversible responsiveness, such as thermo-, acid/base-, and chemo- induced Gel–sol transitions. Furthermore, the result of rheological measurements showed the Gel has an intrinsic self-healing property, and the thixotropic process could be repeated at least three times. Interestingly, when doped with spiropyran molecules, the supramolecular Polymer Gel could also be employed as erasable materials. Thus, these results could be highly anticipated to benefit for further construction of smart materials with high healing efficiency, and ultimately be used in practical application.
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Supramolecular Polymer Gel with multi stimuli responsive, self-healing and erasable properties generated by host–guest interactions
Polymer, 2013Co-Authors: Fei Zeng, Chuanfeng ChenAbstract:Abstract A supramolecular Polymer Gel formed between triptycene-based bis(crown ether) and coPolymer containing dibenzylammonium (DBA) moieties by host–guest interactions was described. We demonstrated the formation of the supramolecular Polymer networks between the bis(crown ether) and the coPolymer by the 1 H NMR spectroscopy and solution viscometry, and we also obtained a colorless and transparent supramolecular Polymer Gel at high concentration. Moreover, the supramolecular Polymer Gel showed multi-stimuli reversible responsiveness, such as thermo-, acid/base-, and chemo- induced Gel–sol transitions. Furthermore, the result of rheological measurements showed the Gel has an intrinsic self-healing property, and the thixotropic process could be repeated at least three times. Interestingly, when doped with spiropyran molecules, the supramolecular Polymer Gel could also be employed as erasable materials. Thus, these results could be highly anticipated to benefit for further construction of smart materials with high healing efficiency, and ultimately be used in practical application.
Melissa L Mather - One of the best experts on this subject based on the ideXlab platform.
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measurement of ultrasonic attenuation coefficient in Polymer Gel dosimeters
Physics in Medicine and Biology, 2003Co-Authors: Melissa L Mather, Paul Charles, Clair BaldockAbstract:A technique is described for investigation of the ultrasonic attenuation coefficient for evaluation of absorbed dose in Polymer Gel dosimeters. Using this technique the attenuation coefficient as a function of absorbed dose in PAG and MAGIC Polymer Gel dosimeters was measured. The ultrasonic attenuation coefficient dose sensitivity for PAG was found to be 2.9 ± 0.3 dB m−1 Gy−1 and for MAGIC Gel 4.2 ± 0.3 dB m−1 Gy−1. Unlike previous studies of ultrasonic attenuation in Polymer Gel dosimeters this technique enables a direct measure of the attenuation coefficient.
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ultrasonic absorption in Polymer Gel dosimeters
Ultrasonics, 2003Co-Authors: Melissa L Mather, A F Collings, Nick Bajenov, Andrew K. Whittaker, Clair BaldockAbstract:Ultrasonic absorption in Polymer Gel dosimeters was investigated. An ultrasonic interferometer was used to study the frequency (f) dependence of the absorption coefficient (alpha) in a polyacrylamide Gel dosimeter (PAG) in the frequency range 5-20 MHz. The frequency dependence of ultrasonic absorption deviated from that of an ideal viscous fluid. The presence of relaxation mechanisms was evidenced by the frequency dependence of alpha/f(2) and the dispersion in ultrasonic velocity. It was concluded that absorption in Polymer Gel dosimeters is due to a number of relaxation processes which may include Polymer-solvent interactions as well as relaxation due to motion of Polymer side groups. The dependence of ultrasonic absorption on absorbed dose and formulation was also investigated in Polymer Gel dosimeters as a function of pH and chemical composition. Changes in dosimeter pH and chemical composition resulted in a variation in ultrasonic dose response curves. The observed dependence on pH was considered to be due to pH induced modifications in the radiation yield while changes in chemical composition resulted in differences in Polymerisation kinetics. (C) 2003 Elsevier B.V. All rights reserved.
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Application of Ultrasound to Polymer Gel Dosimeters used in Radiotherapy
2003Co-Authors: Melissa L MatherAbstract:Recent advances in radiotherapy techniques for treatment of cancer place great demands on radiation dosimetry used for verification of treatments. Polymer Gel dosimeters capable of recording absorbed dose distributions in 3D are being developed for verification of complex radiotherapy treatments. Currently, one of the major challenges in Polymer Gel dosimetry is development of evaluation techniques of absorbed dose distributions capable of the accuracy and spatial resolution necessary for radiotherapy. Current evaluation techniques all suffer from a number of complications that inhibit their acceptance into radiotherapy clinics. A technically simpler and more cost effective evaluation system of Polymer Gel dosimeters is needed. The overall objective of this study was to develop a new evaluation technique of Polymer Gel dosimeters using ultrasound. A comprehensive study of the potential use of ultrasound in Polymer Gel dosimeters was carried out which has demonstrated ultrasound has great potential as an evaluation technique in Polymer Gel dosimetry. A major contribution to the field of Polymer Gel dosimetry was made through the development of a prototype ultrasound scanning system for evaluation of Polymer Gel dosimeters. Significant advances were also made in the understanding of post irradiation changes in Polymer Gel dosimeters that are of importance to the field of Polymer Gel dosimetry. The ultrasound techniques introduced in this study are likely to play a major role in the future of Polymer Gel dosimetry and the main findings of this study are listed as follows:
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investigation of ultrasonic properties of pag and magic Polymer Gel dosimeters
Physics in Medicine and Biology, 2002Co-Authors: Melissa L Mather, Y De Deene, Andrew K. Whittaker, George P Simon, R P G Rutgers, Clair BaldockAbstract:Ultrasonic speed of propagation and attenuation were investigated as a function of absorbed radiation dose in PAG and MAGIC Polymer Gel dosimeters. Both PAG and MAGIC Gel dosimeters displayed a dependence of ultrasonic parameters on absorbed dose with attenuation displaying significant changes in the dose range investigated. The ultrasonic attenuation dose sensitivity at 4 MHz in MAGIC Gels was determined to be 4.7 +/- 0.3 dB m(-1) Gy(-1) and for PAG 3.9 +/- 0.3 dB m(-1) Gy(-1). Ultrasonic speed dose sensitivities were 0.178 +/- 0.006 m s(-1) Gy(-1) for MAGIC Gel and -0.44 +/- 0.02 m s(-1) Gy(-1) for PAG. Density and compressional elastic modulus were investigated to explain the different sensitivities of ultrasonic speed to radiation for PAG and MAGIC Gels. The different sensitivities were found to be due to differences in the compressional elastic modulus as a function of dose for the two formulations. To understand the physical phenomena underlying the increase in ultrasonic attenuation with dose, the viscoelastic properties of the Gels were studied. Results suggest that at ultrasonic frequencies, attenuation in Polymer Gel dosimeters is primarily due to volume viscosity. It is concluded that ultrasonic attenuation significantly increases with absorbed dose. Also, the ultrasonic speed in Polymer Gel dosimeters is affected by changes in dosimeter elastic modulus that are likely to be a result of Polymerization. It is suggested that ultrasound is a sufficiently sensitive technique for Polymer Gel dosimetry.
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a basic study of some normoxic Polymer Gel dosimeters
Physics in Medicine and Biology, 2002Co-Authors: Melissa L Mather, A J Venning, C Hurley, Y De Deene, Brendan Healy, K Vergote, C BaldockAbstract:Polymer Gel dosimeters offer a wide range of potential applications in the three-dimensional verification of complex dose distribution such as in intensity-modulated radiotherapy (IMRT). Until now, however, Polymer Gel dosimeters have not been widely used in the clinic. One of the reasons is that they are difficult to manufacture. As the Polymerization in Polymer Gels is inhibited by oxygen, all free oxygen has to be removed from the Gels. For several years this was achieved by bubbling nitrogen through the Gel solutions and by filling the phantoms in a glove box that is perfused with nitrogen. Recently another Gel formulation was proposed in which oxygen is bound in a metallo-organic complex thus removing the problem of oxygen inhibition. The proposed Gel consists of methacrylic acid, Gelatin, ascorbic acid, hydroquinone and copper(II)sulphate and is given the acronym MAGIC Gel dosimeter. These Gels are fabricated under normal atmospheric conditions and are therefore called 'normoxic' Gel dosimeters. In this study, a chemical analysis on the MAGIC Gel was performed. The composition of the Gel was varied and its radiation response was evaluated. The role of different chemicals and the reaction kinetics are discussed. It was found that ascorbic acid alone was able to bind the oxygen and can thus be used as an anti-oxidant in a Polymer Gel dosimeter. It was also found that the anti-oxidants N-acetyl-cysteine and tetrakis(hydroxymethyl)phosphonium were effective in scavenging the oxygen. However, the rate of oxygen scavenging is dependent on the anti-oxidant and its concentration with tetrakis(hydroxymethyl)phosphonium being the most reactive anti-oxidants. Potentiometric oxygen measurements in solution provide an easy way to get a first impression on the rate of oxygen scavenging. It is shown that cupper(II)sulphate operates as a catalyst in the oxidation of ascorbic acid. We, therefore, propose some new normoxic Gel formulations that have a less complicated chemical formulation than the MAGIC Gel.
Clive Baldock - One of the best experts on this subject based on the ideXlab platform.
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Investigation of the MAGAS normoxic Polymer Gel dosimeter with Pyrex glass walls for clinical radiotherapy dosimetry
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2005Co-Authors: A J Venning, B. Healy, K. N. Nitschke, Clive BaldockAbstract:Abstract Depth doses for a 6 MV photon beam have been measured with the Methacrylic Acid Gelatin with AScorbic acid (MAGAS) Polymer Gel dosimeter contained in a cylindrical Pyrex glass phantom and Pyrex glass tubes and compared with depth doses calculated using Monte Carlo EGS4 code and ionisation chamber measurements in water. Differences between the Polymer Gel, Monte Carlo and ionisation chamber depth doses were up to 4%. Measurements were performed with an ionisation chamber under different thicknesses of Pyrex glass to determine correction factors for the Pyrex glass phantom wall material in the Polymer Gel measurement of depth dose. With radiological depth scaling and correction factors applied, the extent of agreement with ionisation chamber measurements in water was within 3%. The R 2 -dose response of the Polymer Gel in glass vials was linear up to 25 Gy. The MAGAS Polymer Gel dosimeter has shown potential as a clinical radiotherapy tool for the evaluation of depth dose. Further investigation is required to fully develop its capabilities and to reduce differences with measurements made with other dosimetry systems.
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investigation of the pagat Polymer Gel dosimeter using magnetic resonance imaging
Physics in Medicine and Biology, 2005Co-Authors: Brendan Hill, A J Venning, S Brindha, Brendan Healy, Clive BaldockAbstract:Investigation of the normoxic PAGAT Polymer Gel dosimeter has been undertaken. The concentrations of the chemical components of the Gel were varied and its response to ionizing radiation evaluated. Using MRI, the formulation to give the maximum change in the transverse relaxation rate R2 was determined to be 4.5% N, N'–methylene-bis-acrylamide (bis), 4.5% acrylamide (AA), 5% Gelatine, 5 mM tetrakis (hydroxymethyl) phosphonium chloride (THPC), 0.01 mM hydroquinone (HQ) and 86% H2O. The optimal post-manufacture irradiation and post-irradiation imaging times were both determined to be 12 h. The R2-dose response was linear up to 7 Gy with R2-dose sensitivities of (0.183 ± 0.005) s−1 Gy−1, (0.182 ± 0.005) s−1 Gy−1 and (0.192 ± 0.005) s−1 Gy−1 when imaged at 12 h, 7 days and 24 days post-irradiation, respectively. The R2-dose sensitivities were within the range of previously published values for the hypoxic PAG formulations. For the imaging parameters used in this study the optimum dose resolution was achieved for low doses. The normalized R2 edge response showed a high degree of spatial stability over a 24 day period. This study has shown that the normoxic PAGAT Polymer Gel has the properties of a dosimetric tool, which can be used in clinical radiotherapy. The PAGAT Polymer Gel has been shown to have similar qualities to the PAG Polymer Gel, while offering the significant advantage of simplification of the manufacturing procedure.
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Investigation of the MAGAS normoxic Polymer Gel dosimeter with Pyrex glass walls for clinical radiotherapy dosimetry
Nuclear Instruments and Methods in Physics Research Section A: Accelerators Spectrometers Detectors and Associated Equipment, 2005Co-Authors: A J Venning, B. Healy, K. N. Nitschke, Clive BaldockAbstract:Depth doses for a 6 MV photon beam have been measured with the Methacrylic Acid Gelatin with AScorbic acid (MAGAS) Polymer Gel dosimeter contained in a cylindrical Pyrex glass phantom and Pyrex glass tubes and compared with depth doses calculated using Monte Carlo EGS4 code and ionisation chamber measurements in water. Differences between the Polymer Gel, Monte Carlo and ionisation chamber depth doses were up to 4%. Measurements were performed with an ionisation chamber under different thicknesses of Pyrex glass to determine correction factors for the Pyrex glass phantom wall material in the Polymer Gel measurement of depth dose. With radiological depth scaling and correction factors applied, the extent of agreement with ionisation chamber measurements in water was within 3%. The R2-dose response of the Polymer Gel in glass vials was linear up to 25 Gy. The MAGAS Polymer Gel dosimeter has shown potential as a clinical radiotherapy tool for the evaluation of depth dose. Further investigation is required to fully develop its capabilities and to reduce differences with measurements made with other dosimetry systems.7 page(s
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Radiological attenuation properties of normoxic Polymer Gel dosimeters
Journal of Physics: Conference Series, 2004Co-Authors: S Brindha, Brendan Hill, A J Venning, Clive BaldockAbstract:Since the development of normoxic Gels several others have been evaluated for dose response and spatial stability with MRI. Tetrakis (hydroxymethyl) phosphonium chloride (THP) has been used as an oxygen scavenger in MAGAT and PAGAT Polymer Gel dosimeters. X-ray CT has been used as an evaluation tool to measure dose response and dose distributions of irradiated Polymer Gel dosimeters. In this work the radiological attenuation properties of the PAGAT and MAGAT normoxic Polymer Gels are investigated as part of a feasibility study in using x-ray CT as an evaluation tool for normoxic Polymer Gel dosimeters.
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Use of normoxic Polymer Gel dosimeters for measuring diagnostic doses on CT scanners
Journal of Physics: Conference Series, 2004Co-Authors: Brendan Hill, A J Venning, Clive BaldockAbstract:X-ray CT has been used to evaluate Polymer Gel dosimeters for dose response in the therapeutic dose range. This method of Polymer Gel dosimeter evaluation has been shown to be useful for instance in the comparison of complex sterotactic field distributions with treatment plans. Image averaging and subtraction techniques are used for noise reduction in Polymer Gel dosimeters resulting in the delivery of several CT slices across the Polymer Gel dosimeters. It was a logical progression to evaluate normoxic Polymer Gel dosimeters with optimized CT scanning protocols. During these investigations it was found that unirradiated regions in irradiated normoxic Polymer Gel dosimetry phantoms Polymerised possibly as a result of the evaluation using CT. This prompted an investigation of the CT diagnostic dose response of the normoxic Polymer Gel dosimeter in order to determine the dose contribution when evaluated using a CT scanner. Having established that there was an effect on the normoxic Polymer Gel dosimeter when evaluating with a CT scanner the suitability of these Gels in the determination of CT diagnostic dose measurement was further investigated.