On The Development Of Absorbed Dose Calorimeter Systems For Absolute Clinical Dosimetry
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| Author | : James Renaud |
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| Total Pages | : |
| Release | : 2017 |
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"The aim of this work is to develop and evaluate the feasibility of absolute dose to water measurements in clinical high-energy photon, electron, and proton beams using a probe format graphite calorimeter (GPC; a.k.a. Aerrow), a sealed electron water calorimeter (ESWcal), and a short range water calorimeter (SHREWcal). Measurements were performed using these calorimeters, all of which were designed and built in-house, and ionization chambers with calibrations traceable to national primary dose standards. A sealed glass vessel constructed at the National Research Council of Canada (NRC) was used as part of the water calorimeter experiments. Calorimeter-based dose results were validated in high-energy photon beams against established dose standards. A finite element analysis software package was used to numerically solve the heat transport equation in models of the calorimeters used throughout this project. Monte Carlo radiation transport codes were used to calculate the perturbation factors accounting for the presence of non water (or graphite) detector materials in the path of the beam. For the GPC, absolute dose output measurements were performed using its two independent modes of operation for several clinical high-energy photon and electron beams, in addition to a relative characterization of the detector. For the ESWcal, electron beam quality conversion factors were directly measured for two types of ionization chambers. For the SHREWcal, dose measurements were performed for clinical short-range electron beams and cyclotron-based monoenergetic and modulated proton beams. Absorbed doses measured using both GPC modes of operation were found to agree with chamber-derived doses to well within the combined uncertainty of about 1.5 %. Moreover, the detector was characterized as having a strong linear response in the range of 80 cGy to 470 cGy, and no dependence upon dose rate in the range of 0.5 Gy/min to 5.4 Gy/min. For photon and electron beam qualities in the range of 58.4 %
| Author | : James Renaud |
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| Release | : 2012 |
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"In this work, the feasibility of absolute dose to water measurements using a small scale graphite probe calorimeter (GPC) in a clinical environment is established. A numerical design optimization study was conducted by simulating the heat transfer in the GPC resulting from irradiation using a finite element method software package. The choice of device shape, dimensions and materials was made to minimize the heat loss in the sensitive volume of the GPC. The resulting design, which incorporates a novel aerogel-based thermal insulator, was built in-house. Absorbed dose to water measurements were made under standard conditions in a 6 MV 1000 MU/min photon beam and subsequently compared against TG-51 derived values. The average measured dose to water was 95.7 ± 1.4 cGy/100 MU, as compared to an expected value of 96.6 cGy/100 MU. The Monte Carlo-calculated graphite to water dose conversion factor was 1.099, while the derived heat loss correction factors varied between 1.005 and 1.013. The most significant sources of uncertainty were the repeatability (type A, 1.4%) and thermistor calibration (type B, 2.1%). The contribution of these factors to the overall uncertainty is expected to decrease significantly upon the implementation of active thermal stabilization provided by a temperature controller and direct electrical calibration, respectively. This proof of concept demonstrates the feasibility of using the GPC as a practical clinical absolute photon dosimeter and lays the foundation for a miniaturized version suitable for small and composite field dosimetry." --
| Author | : |
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| Release | : 1979 |
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The dosimetric studies at this laboratory were initiated with the primary goal of developing systems for the determination of absorbed dose in biological research and clinical applications. The primary method under study is the local absorbed dose calorimeter, a concept initiated and developed by J.S. Laughlin. In addition, secondary dosimetric systems such as ionization chambers, chemical dosimeters and thermoluminescent dosimeters (TLD) are being developed and applied to provide an absolute basis for the evaluation and comparison of experiments, treatments, and other procedures using radiation.
| Author | : Ben Petree |
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| Total Pages | : 56 |
| Release | : 1962 |
| Genre | : Calorimeters |
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| Author | : Benjamin Côté |
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| Total Pages | : |
| Release | : 2020 |
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"The aim of this work is to adapt the previously developed graphite probe absorbed dose calorimeter (GPC, a.k.a. Aerrow) to be able to perform accurate and precise dosimetry in the smallest irradiation field size used in external beam radiotherapy. Using a scaled-down version of the previous Aerrow, Aerrow-mini was designed with a cylindrical sensitive volume with a radius of 3 mm and a length of 5 mm making the volume equal to 0.146 cm3. Dose deposition Monte Carlo simulations were performed to calculate "k" _("Q" _"clin" "," "Q" _"msr" )^("f" _"clin" "," "f" _"msr" ) and quantify the behavior at small fields. Using those results, the thermal insulating material was chosen to be the Airloy X103 at 0.4 g/cm3, making the correction for small fields less than ± 1 % throughout all field sizes. After building a prototype in-house, the probe was used in isothermal mode to perform dose measurement. The shape of the probe signal was not as expected. Further investigations were performed, but because of a lost connection on the heating side, the isothermal mode was disabled. Measurements were then performed using the adiabatic mode in a thermally stable phantom. Once again, unexpected shaped signals were measured. An alternative analysis method that uses the dose rate information to calculate the total received dose was proposed rather than the commonly used temperature offset technique. Dose measurements were performed with the Aerrow-mini and compared with an Exradin A1SL ionization chamber with three beams: (1) 10 MV FFF beam at 2400 MU/min at 10 × 10 cm2, (2) 6 MV FFF beam at 1400 MU/min at 10 × 10 cm2, and (3) 10 MV FFF beam at 2400 MU/min at 2 × 2 cm2. Dose differences of 0.4 %, 0.5% and 0.1 % were obtained for the beam (1), (2) and (3) respectively. These results suggest the validity of the Monte Carlo model and the newly proposed way of isothermal analysis"--
| Author | : Jan P. Seuntjens |
| Publisher | : Medical Physics Publishing Corporation |
| Total Pages | : 368 |
| Release | : 2002 |
| Genre | : Medical |
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| Author | : International Commission on Radiological Units and Measurements |
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| Total Pages | : 78 |
| Release | : 1963 |
| Genre | : Radiation |
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| Author | : Kristin J. Stewart |
| Publisher | : |
| Total Pages | : 224 |
| Release | : 2007 |
| Genre | : Calorimeters |
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"In this work we developed two new devices that aim to improve the accuracy of relative and reference dosimetry for radiation therapy: a guarded liquid ionization chamber (GLIC) and an electron sealed water (ESW) calorimeter. With the GLIC we aimed to develop a perturbation-free energy-independent detector with high spatial resolution for relative dosimetry. We achieved sufficient stability for short-term measurements using the GLIC-03, which has a sensitive volume of approximately 2 mm3. We evaluated ion recombination in pulsed photon beams using a theoretical model and also determined a new empirical method to correct for relative differences in general recombination which could be used in cases where the theoretical model was not applicable. The energy dependence of the GLIC-03 was 1.1% between 6 and 18 MV photon beams. Measurements in the build-up region of an 18 MV beam indicated that this detector produces minimal perturbation to the radiation field and confirmed the validity of the empirical recombination correction. The ESW calorimeter was designed to directly measure absorbed dose to water in clinical electron beams. We obtained reproducible measurements for 6 to 20 MeV beams. We determined corrections for perturbations to the radiation field caused by the glass calorimeter vessel and for conductive heat transfer due to the dose gradient and non-water materials. The overall uncertainty on the ESW calorimeter dose was 0.5% for the 9 to 20 MeV beams and 1.0% for 6 MeV, showing for the first time that the development of a water-calorimeter-based standard for electron beams over a wide range of energies is feasible. Comparison between measurements with the ESW calorimeter and the NRC photon beam standard calorimeter in a 6 MeV beam revealed a discrepancy of 0.7℗ł0.2% which is still under investigation. Absorbed-dose beam quality conversion factors in electron beams were measured using the ESW calorimeter for the Exradin A12 and PTW Roos ionization" --
| Author | : International Atomic Energy Agency |
| Publisher | : |
| Total Pages | : 260 |
| Release | : 2000 |
| Genre | : Medical |
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This Code of Practice, which has also been endorsed by WHO, PAHO and ESTRO, fulfils the need for a systematic and internationally unified approach to the calibration of ionization chambers in terms of absorbed dose to water and to the use of these detectors in determining the absorbed dose to water for the radiation beams used in radiotherapy. It provides a methodology for the determination of absorbed dose to water in the low, medium and high energy photon beams, electron beams, proton beams and heavy ion beams used for external radiation therapy.
| Author | : Niels W. Holm |
| Publisher | : |
| Total Pages | : 63 |
| Release | : 1964 |
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This report describes the use of a 10-ounce Thermos flask, filled with water, for absolute standardization of a Megacurie Co-60 source. Once the absorbed dose rate is established in a given position relative to the source, other aqueous solutions can be irradiated with an identical, and known, dose. The radiochemical (or radiobiological) yield can thus be readily determined. A short discussion is given on the concepts of radiation calorimetry, and experimental findings are reported for several modes of operating this particular device. It is shown that a set of electrical calibrations combined with a set of irradiations, both carried out in a constant temperature environment, can give complete information on the properties of the calorimeter and the absorbed dose rate. Furthermore, it is shown that once these properties are established, the calorimeter can be operated in a simplified adiabatic mode for determining the absorbed dose rate in other locations or sources. The accuracy of the method is discussed, and application of the system for calibration of chemical dosimeters is suggested. (Author).
