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Bian J, Duran J, Shin WG, Ramos-Méndez J, Sankey JC, Childress L, Seuntjens J, Enger SA. GEANT4-DNA simulation of temperature-dependent and pH-dependent yields of chemical radiolytic species. Phys Med Biol 2023; 68:124002. [PMID: 37230081 DOI: 10.1088/1361-6560/acd90d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Accepted: 05/25/2023] [Indexed: 05/27/2023]
Abstract
Objective.GEANT4-DNA can simulate radiation chemical yield (G-value) for radiolytic species such as the hydrated electron (eaq-) with the independent reaction times (IRT) method, however, only at room temperature and neutral pH. This work aims to modify the GEANT4-DNA source code to enable the calculation ofG-values for radiolytic species at different temperatures and pH values.Approach.In the GEANT4-DNA source code, values of chemical parameters such as reaction rate constant, diffusion coefficient, Onsager radius, and water density were replaced by corresponding temperature-dependent polynomials. The initial concentration of hydrogen ion (H+)/hydronium ion (H3O+) was scaled for a desired pH using the relationship pH = -log10[H+]. To validate our modifications, two sets of simulations were performed. (A) A water cube with 1.0 km sides and a pH of 7 was irradiated with an isotropic electron source of 1 MeV. The end time was 1μs. The temperatures varied from 25 °C to 150 °C. (B) The same setup as (A) was used, however, the temperature was set to 25 °C while the pH varied from 5 to 9. The results were compared with published experimental and simulated work.Main results.The IRT method in GEANT4-DNA was successfully modified to simulateG-values for radiolytic species at different temperatures and pH values. Our temperature-dependent results agreed with experimental data within 0.64%-9.79%, and with simulated data within 3.52%-12.47%. The pH-dependent results agreed well with experimental data within 0.52% to 3.19% except at a pH of 5 (15.99%) and with simulated data within 4.40%-5.53%. The uncertainties were below ±0.20%. Overall our results agreed better with experimental than simulation data.Significance.Modifications in the GEANT4-DNA code enabled the calculation ofG-values for radiolytic species at different temperatures and pH values.
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Affiliation(s)
- Jingyi Bian
- Medical Physics Unit, Department of Oncology, Faculty of Medicine, McGill University, Montreal, Quebec, Canada
| | - Juan Duran
- Medical Physics Unit, Department of Oncology, Faculty of Medicine, McGill University, Montreal, Quebec, Canada
| | - Wook-Geun Shin
- Physics Division, Department of Radiation Oncology, Massachusetts General Hospital & Harvard Medical School, Boston, MA-02114, United States of America
| | - Jose Ramos-Méndez
- Department of Radiation Oncology, University of California San Francisco, CA, United States of America
| | - Jack C Sankey
- Department of Physics, McGill University, Montreal, Quebec, Canada
| | - Lilian Childress
- Department of Physics, McGill University, Montreal, Quebec, Canada
| | - Jan Seuntjens
- Medical Physics Unit, Department of Oncology, Faculty of Medicine, McGill University, Montreal, Quebec, Canada
- Research Institute of the McGill University Health Centre, Montreal, Quebec, Canada
| | - Shirin A Enger
- Medical Physics Unit, Department of Oncology, Faculty of Medicine, McGill University, Montreal, Quebec, Canada
- Research Institute of the McGill University Health Centre, Montreal, Quebec, Canada
- Lady Davis Institute for Medical Research, Jewish General Hospital, Montreal, Quebec, Canada
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Huart L, Nicolas C, Hervé du Penhoat MA, Guigner JM, Gosse C, Palaudoux J, Lefrançois S, Mercere P, Dasilva P, Renault JP, Chevallard C. A microfluidic dosimetry cell to irradiate solutions with poorly penetrating radiations: a step towards online dosimetry for synchrotron beamlines. JOURNAL OF SYNCHROTRON RADIATION 2021; 28:778-789. [PMID: 33949986 PMCID: PMC8127378 DOI: 10.1107/s1600577521002691] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Accepted: 03/11/2021] [Indexed: 05/21/2023]
Abstract
Synchrotron radiation can induce sample damage, whether intended or not. In the case of sensitive samples, such as biological ones, modifications can be significant. To understand and predict the effects due to exposure, it is necessary to know the ionizing radiation dose deposited in the sample. In the case of aqueous samples, deleterious effects are mostly induced by the production of reactive oxygen species via water radiolysis. These species are therefore good indicators of the dose. Here the application of a microfluidic cell specifically optimized for low penetrating soft X-ray radiation is reported. Sodium benzoate was used as a fluorescent dosimeter thanks to its specific detection of hydroxyl radicals, a radiolytic product of water. Measurements at 1.28 keV led to the determination of a hydroxyl production yield, G(HO.), of 0.025 ± 0.004 µmol J-1. This result is in agreement with the literature and confirms the high linear energy transfer behavior of soft X-rays. An analysis of the important parameters of the microfluidic dosimetry cell, as well as their influences over dosimetry, is also reported.
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Affiliation(s)
- Lucie Huart
- Université Paris-Saclay, CEA, CNRS, NIMBE, 91191 Gif-sur-Yvette, France
- IMPMC, Sorbonne Université, UMR CNRS 7590, MNHN, 75005 Paris, France
- Synchrotron SOLEIL, 91 192 Saint Aubin, France
| | | | | | | | - Charlie Gosse
- Institut de Biologie de l’Ecole Normale Supérieure, ENS, CNRS, INSERM, PSL Research University, 75005 Paris, France
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Bouchard H. Reference dosimetry of modulated and dynamic photon beams. Phys Med Biol 2021; 65:24TR05. [PMID: 33438582 DOI: 10.1088/1361-6560/abc3fb] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
In the late 1980s, a new technique was proposed that would revolutionize radiotherapy. Now referred to as intensity-modulated radiotherapy, it is at the core of state-of-the-art photon beam delivery techniques, such as helical tomotherapy and volumetric modulated arc therapy. Despite over two decades of clinical application, there are still no established guidelines on the calibration of dynamic modulated photon beams. In 2008, the IAEA-AAPM work group on nonstandard photon beam dosimetry published a formalism to support the development of a new generation of protocols applicable to nonstandard beam reference dosimetry (Alfonso et al 2008 Med. Phys. 35 5179-86). The recent IAEA Code of Practice TRS-483 was published as a result of this initiative and addresses exclusively small static beams. But the plan-class specific reference calibration route proposed by Alfonso et al (2008 Med. Phys. 35 5179-86) is a change of paradigm that is yet to be implemented in radiotherapy clinics. The main goals of this paper are to provide a literature review on the dosimetry of nonstandard photon beams, including dynamic deliveries, and to discuss anticipated benefits and challenges in a future implementation of the IAEA-AAPM formalism on dynamic photon beams.
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Affiliation(s)
- Hugo Bouchard
- Département de physique, Université de Montréal, Complexe des sciences, 1375 Avenue Thérèse-Lavoie-Roux, Montréal, Québec H2V 0B3, Canada. Centre de recherche du Centre hospitalier de l'Université de Montréal, 900 Rue Saint-Denis, Montréal, Québec H2X 0A9, Canada. Département de radio-oncologie, Centre hospitalier de l'Université de Montréal (CHUM), 1051 Rue Sanguinet, Montréal, Québec H2X 3E4, Canada
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Krauss A, Spindeldreier CK, Klüter S. Direct determination of [Formula: see text] for cylindrical ionization chambers in a 6 MV 0.35 T MR-linac. Phys Med Biol 2020; 65:235049. [PMID: 33300501 DOI: 10.1088/1361-6560/abab56] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
To ensure accurate reference dosimetry with ionization chambers in magnetic resonance linear accelerators (MR-linacs), the influence of the magnetic field on the response of the ionization chambers must be considered. The most direct method considering the influence of magnetic fields in dosimetry is to apply an appropriate absorbed-dose-to-water primary standard. At PTB, a new water calorimeter has been designed which is capable to determine Dw,Q in an MR-linac. The new device allows the direct calibration of ionization chambers in terms of absorbed dose to water for MR-linac irradiation conditions. Hence, the correction factors [Formula: see text] can be determined which replace the current radiation-quality dependent correction factors [Formula: see text] for dosimetry in the presence of magnetic fields. In cooperation with Heidelberg University Hospital,[Formula: see text] factors were measured at the 6 MV 0.35 T Viewray MR-linac for different cylindrical ionization chambers with sensitive volumes ranging from 0.015 cm3 to 0.65 cm3. The chambers were placed both perpendicular and parallel in respect to the magnetic field. Standard uncertainties of about 0.5% were achieved.
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Affiliation(s)
- A Krauss
- Department of Dosimetry for Radiation Therapy and Diagnostic Radiology, Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, D-38116, Braunschweig, Germany
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Renaud J, Palmans H, Sarfehnia A, Seuntjens J. Absorbed dose calorimetry. ACTA ACUST UNITED AC 2020; 65:05TR02. [DOI: 10.1088/1361-6560/ab4f29] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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Guesmi S, Raouafi A, Amri I, Hamzaoui AH, Boulila A, Hosni F, Sghaier H. Polyphenolic extracts from the xerophyte Rhamnus lycioides as a radiation biodosimeter. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2020; 27:5661-5669. [PMID: 30484056 DOI: 10.1007/s11356-018-3709-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2018] [Accepted: 11/06/2018] [Indexed: 06/09/2023]
Abstract
The majority of dosimeters currently in use are synthetic and very expensive. Therefore, the study of the dosimetric characteristics of polyphenolic extracts of xerophytes is useful because drought stress causes an increase in the production of these cheap and natural compounds containing benzene rings. Here, the polyphenolic compounds were extracted from Rhamnus lycioides which was collected from Bou-Hedma National Park in Tunisia and identified using liquid chromatography-mass spectrometry (LC-MS). We investigated the impact of cobalt-60 (60Co) irradiation (0-30 kilogray (kGy)) on the color parameters of polyphenolic extracts of R. lycioides using the Konica Minolta CR 300 portable colorimeter and UV-Visible spectroscopy. The structural and morphological characteristics of the irradiated extracts were assessed using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) technique and scanning electron microscopy (SEM). Overall, our results suggest that exposure to ionizing radiation (IR) of the polyphenolic components of the xerophyte R. lycioides has produced significant dose-dependent changes in their optical and morphological properties. Thus, these extracts can be valorized as biodosimeters in the dose range from 5 to 25 kGy.
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Affiliation(s)
- Sihem Guesmi
- National Agronomic Institute of Tunisia (INAT), 43, Avenue Charles Nicolle, Mahrajène, 1082, Tunis, Tunisia.
- Laboratory "Energy and Matter for Development of Nuclear Sciences" (LR16CNSTN02), National Center for Nuclear Sciences and Technology, Sidi Thabet Technopark, 2020, Sidi Thabet, Tunisia.
| | - Amel Raouafi
- Laboratory "Energy and Matter for Development of Nuclear Sciences" (LR16CNSTN02), National Center for Nuclear Sciences and Technology, Sidi Thabet Technopark, 2020, Sidi Thabet, Tunisia
| | - Ismail Amri
- Laboratoire d'Ecologie et d'Amélioration Sylvo-Pastorale, Institut National de Recherches en Genie Rural, Ariana, Tunisia
| | - Ahmed Hicham Hamzaoui
- Laboratory of Useful Materials Valuation, National Center for Research in Materials Sciences, Borj Cedria Technopark, BP 73, 8027, Soliman, Tunisia
| | - Abdennacer Boulila
- Laboratory of Natural Substances (LR10INRAP02), National Institute of Research and Physico-chemical Analyses, Biotech Pole of Sidi Thabet, Ariana, Tunisia
| | - Faouzi Hosni
- Laboratory "Energy and Matter for Development of Nuclear Sciences" (LR16CNSTN02), National Center for Nuclear Sciences and Technology, Sidi Thabet Technopark, 2020, Sidi Thabet, Tunisia
- Faculty of Sciences, Bisha University, Bisha, Kingdom of Saudi Arabia
| | - Haitham Sghaier
- Laboratory "Energy and Matter for Development of Nuclear Sciences" (LR16CNSTN02), National Center for Nuclear Sciences and Technology, Sidi Thabet Technopark, 2020, Sidi Thabet, Tunisia.
- Associated with Laboratory "Biotechnology and Nuclear Technology" (LR16CNSTN01) and Laboratory "Biotechnology and Bio-Geo Resources Valorization" (LR11ES31), Sidi Thabet Technopark, 2020, Sidi Thabet, Tunisia.
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Sife-Eldeen KA. A possible ɤ- radiation Dosimeter based on the radiation induced changes in Electrical conductivity of water in the presence of silica gel. JOURNAL OF RADIATION RESEARCH AND APPLIED SCIENCES 2020. [DOI: 10.1080/16878507.2020.1744332] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Abstract
For the past several decades, synchrotron radiation has been extensively used to measure the spatial distribution and chemical affinity of elements found in trace concentrations (<few μg/g) in animal and human tissues. Intense and highly focused (lateral size of several micrometers) X-ray beams combined with small steps of photon energy tuning (2-3 eV) of synchrotron radiation allowed X-ray fluorescence (XRF) and X-ray absorption spectroscopy (XAS) techniques to nondestructively and simultaneously detect trace elements as well as identify their chemical affinity and speciation in situ, respectively. Although limited by measurement time and radiation damage to the tissue, these techniques are commonly used to obtain two-dimensional and three-dimensional maps of several elements at synchrotron facilities around the world. The spatial distribution and chemistry of the trace elements obtained is then correlated to the targeted anatomical structures and to the biological functions (normal or pathological). For example, synchrotron-based in vitro studies of various human tissues showed significant differences between the normal and pathological distributions of metallic trace elements such as iron, zinc, copper, and lead in relation to human diseases ranging from Parkinson's disease and cancer to osteoporosis and osteoarthritis. Current research effort is aimed at not only measuring the abnormal elemental distributions associated with various diseases, but also indicate or discover possible biological mechanisms that could explain such observations. While a number of studies confirmed and strengthened previous knowledge, others revealed or suggested new possible roles of trace elements or provided a more accurate spatial distribution in relation to the underlying histology. This area of research is at the intersection of several current fundamental and applied scientific inquiries such as metabolomics, medicine, biochemistry, toxicology, food science, health physics, and environmental and public health.
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Optical-Radiation-Calorimeter Refinement by Virtual-Sensitivity Analysis. SENSORS 2019; 19:s19051167. [PMID: 30866546 PMCID: PMC6427801 DOI: 10.3390/s19051167] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/25/2019] [Revised: 02/26/2019] [Accepted: 02/26/2019] [Indexed: 11/16/2022]
Abstract
Digital holographic interferometry (DHI) radiation dosimetry has been proposed as an experimental metrology technique for measuring absorbed radiation doses to water with high spatial resolution via noninvasive optical calorimetry. The process involves digitally recording consecutive interference patterns resulting from variations in the refractive index as a function of the radiation-absorbed dose. Experiments conducted on prototype optical systems revealed the approach to be feasible but strongly dependent on environmental-influence quantities and setup configuration. A virtual dosimeter reflecting the prototype was created in a commercial optical modelling package. A number of virtual phantoms were developed to characterize the performance of the dosimeter under ideal conditions and with simulated disruptions in environmental-influence quantities, such as atmospheric and temperature perturbations as well as mechanical vibrations. Investigations into the error response revealed that slow drifts in atmospheric parameters and heat expansion caused the measured dose to vary between measurements, while atmospheric fluctuations and vibration contributed to system noise, significantly lowering the spatial resolution of the detector system. The impact of these effects was found to be largely mitigated with equalisation of the dosimeter's reference and object path lengths, and by miniaturising the detector. Equalising path lengths resulted in a reduction of 97.5% and 96.9% in dosimetric error introduced by heat expansion and atmospheric drift, respectively, while miniaturisation of the dosimeter was found to reduce its sensitivity to vibrations and atmospheric turbulence by up to 41.7% and 54.5%, respectively. This work represents a novel approach to optical-detector refinement in which metrics from medical imaging were adapted into software and applied to a a virtual-detector system. This methodology was found to be well-suited for the optimization of a digital holographic interferometer.
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10
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Obodovskiy I. Radiation Detection. RADIATION 2019. [DOI: 10.1016/b978-0-444-63979-0.00014-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
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11
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Hickling S, Hobson M, El Naqa I. Characterization of X-Ray Acoustic Computed Tomography for Applications in Radiotherapy Dosimetry. IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES 2018. [DOI: 10.1109/trpms.2018.2801724] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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12
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Krauss A, Kapsch RP. Direct determination ofkQfactors for cylindrical and plane-parallel ionization chambers in high-energy electron beams from 6 MeV to 20 MeV. ACTA ACUST UNITED AC 2018; 63:035041. [DOI: 10.1088/1361-6560/aaa71e] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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13
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Osinga-Blättermann JM, Brons S, Greilich S, Jäkel O, Krauss A. Direct determination of k Q for Farmer-type ionization chambers in a clinical scanned carbon ion beam using water calorimetry. Phys Med Biol 2017; 62:2033-2054. [DOI: 10.1088/1361-6560/aa5bac] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Hickling S, Lei H, Hobson M, Léger P, Wang X, El Naqa I. Experimental evaluation of x-ray acoustic computed tomography for radiotherapy dosimetry applications. Med Phys 2017; 44:608-617. [PMID: 28121381 DOI: 10.1002/mp.12039] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Revised: 11/25/2016] [Accepted: 11/29/2016] [Indexed: 12/31/2022] Open
Abstract
PURPOSE The aim of this work was to experimentally demonstrate the feasibility of x-ray acoustic computed tomography (XACT) as a dosimetry tool in a clinical radiotherapy environment. METHODS The acoustic waves induced following a single pulse of linear accelerator irradiation in a water tank were detected with an immersion ultrasound transducer. By rotating the collimator and keeping the transducer stationary, acoustic signals at varying angles surrounding the field were detected and reconstructed to form an XACT image. Simulated XACT images were obtained using a previously developed simulation workflow. Profiles extracted from experimental and simulated XACT images were compared to profiles measured with an ion chamber. A variety of radiation field sizes and shapes were investigated. RESULTS XACT images resembling the geometry of the delivered radiation field were obtained for fields ranging from simple squares to more complex shapes. When comparing profiles extracted from simulated and experimental XACT images of a 4 cm × 4 cm field, 97% of points were found to pass a 3%/3 mm gamma test. Agreement between simulated and experimental XACT images worsened when comparing fields with fine details. Profiles extracted from experimental XACT images were compared to profiles obtained through clinical ion chamber measurements, confirming that the intensity of XACT images is related to deposited radiation dose. Seventy-seven percent of the points in a profile extracted from an experimental XACT image of a 4 cm × 4 cm field passed a 7%/4 mm gamma test when compared to an ion chamber measured profile. In a complicated puzzle-piece shaped field, 86% of the points in an XACT extracted profile passed a 7%/4 mm gamma test. CONCLUSIONS XACT images with intensity related to the spatial distribution of deposited dose in a water tank were formed for a variety of field sizes and shapes. XACT has the potential to be a useful tool for absolute, relative and in vivo dosimetry.
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Affiliation(s)
- Susannah Hickling
- Department of Physics and Medical Physics Unit, McGill University, Cedars Cancer Centre, Montreal, QC, Canada, H4A 3J1
| | - Hao Lei
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Maritza Hobson
- Medical Physics Unit, McGill University Health Centre, Cedars Cancer Centre, Montreal, QC, H4A 3J1, Canada
| | - Pierre Léger
- Medical Physics Unit, McGill University Health Centre, Cedars Cancer Centre, Montreal, QC, H4A 3J1, Canada
| | - Xueding Wang
- Departments of Radiology and Biomedical Engineering, University of Michigan, Ann Arbor, MI, 48109-0600, USA
| | - Issam El Naqa
- Department of Radiation Oncology, University of Michigan, Ann Arbor, MI, 48103-4943, USA
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Flores-Martinez E, Malin MJ, DeWerd LA. Development and characterization of an interferometer for calorimeter-based absorbed dose to water measurements in a medical linear accelerator. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2016; 87:114301. [PMID: 27910378 DOI: 10.1063/1.4967490] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The quantity of relevance for external beam radiotherapy is absorbed dose to water (ADW). An interferometer was built, characterized, and tested to measure ADW within the dose range of interest for external beam radiotherapy using the temperature dependence of the refractive index of water. The interferometer was used to measure radiation-induced phase shifts of a laser beam passing through a (10 × 10 × 10) cm3 water-filled glass phantom, irradiated with a 6 MV photon beam from a medical linear accelerator. The field size was (7 × 7) cm2 and the dose was measured at a depth of 5 cm in the water phantom. The intensity of the interference pattern was measured with a photodiode and was used to calculate the time-dependent phase shift curve. The system was thermally insulated to achieve temperature drifts of less than 1.5 mK/min. Data were acquired 60 s before and after the irradiation. The radiation-induced phase shifts were calculated by taking the difference in the pre- and post-irradiation drifts extrapolated to the midpoint of the irradiation. For 200, 300, and 400 monitor units, the measured doses were 1.6 ± 0.3, 2.6 ± 0.3, and 3.1 ± 0.3 Gy, respectively. Measurements agreed within the uncertainty with dose calculations performed with a treatment planning system. The estimated type-A, k = 1 uncertainty in the measured doses was 0.3 Gy which is an order of magnitude lower than previously published interferometer-based ADW measurements.
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Affiliation(s)
- Everardo Flores-Martinez
- Department of Medical Physics, University of Wisconsin-Madison School of Medicine and Public Health, Madison, Wisconsin 53705, USA
| | - Martha J Malin
- Department of Medical Physics, University of Wisconsin-Madison School of Medicine and Public Health, Madison, Wisconsin 53705, USA
| | - Larry A DeWerd
- Department of Medical Physics, University of Wisconsin-Madison School of Medicine and Public Health, Madison, Wisconsin 53705, USA
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Kron T, Lehmann J, Greer PB. Dosimetry of ionising radiation in modern radiation oncology. Phys Med Biol 2016; 61:R167-205. [DOI: 10.1088/0031-9155/61/14/r167] [Citation(s) in RCA: 68] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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de Prez L, de Pooter J, Jansen B, Aalbers T. A water calorimeter for on-site absorbed dose to water calibrations in60Co and MV-photon beams including MRI incorporated treatment equipment. Phys Med Biol 2016; 61:5051-76. [DOI: 10.1088/0031-9155/61/13/5051] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Sander T. Air kerma and absorbed dose standards for reference dosimetry in brachytherapy. Br J Radiol 2014; 87:20140176. [PMID: 24814696 PMCID: PMC4453150 DOI: 10.1259/bjr.20140176] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2014] [Revised: 05/07/2014] [Accepted: 05/08/2014] [Indexed: 11/05/2022] Open
Abstract
This article reviews recent developments in primary standards for the calibration of brachytherapy sources, with an emphasis on the currently most common photon-emitting radionuclides. The introduction discusses the need for reference dosimetry in brachytherapy in general. The following section focuses on the three main quantities, i.e. reference air kerma rate, air kerma strength and absorbed dose rate to water, which are currently used for the specification of brachytherapy photon sources and which can be realized with primary standards from first principles. An overview of different air kerma and absorbed dose standards, which have been independently developed by various national metrology institutes over the past two decades, is given in the next two sections. Other dosimetry techniques for brachytherapy will also be discussed. The review closes with an outlook on a possible transition from air kerma to absorbed dose to water-based calibrations for brachytherapy sources in the future.
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Affiliation(s)
- T Sander
- Acoustics and Ionising Radiation, National Physical Laboratory, Teddington, Middlesex, UK
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Krauss A, Kapsch RP. Experimental determination ofkQfactors for cylindrical ionization chambers in 10 cm × 10 cm and 3 cm × 3 cm photon beams from 4 MV to 25 MV. Phys Med Biol 2014; 59:4227-46. [DOI: 10.1088/0031-9155/59/15/4227] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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20
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Cavan A, Meyer J. Digital holographic interferometry: A novel optical calorimetry technique for radiation dosimetry. Med Phys 2014; 41:022102. [DOI: 10.1118/1.4861822] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Rapp B, Perichon N, Denoziere M, Daures J, Ostrowsky A, Bordy JM. The LNE-LNHB water calorimeter for primary measurement of absorbed dose at low depth in water: application to medium-energy x-rays. Phys Med Biol 2013; 58:2769-86. [DOI: 10.1088/0031-9155/58/9/2769] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Perichon N, Rapp B, Denoziere M, Daures J, Ostrowsky A, Bordy JM. Comparison between absorbed dose to water standards established by water calorimetry at the LNE-LNHB and by application of international air-kerma based protocols for kilovoltage medium energy x-rays. Phys Med Biol 2013; 58:2787-806. [DOI: 10.1088/0031-9155/58/9/2787] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Krauss A, Büermann L, Kramer HM, Selbach HJ. Calorimetric determination of the absorbed dose to water for medium-energy x-rays with generating voltages from 70 to 280 kV. Phys Med Biol 2012; 57:6245-68. [DOI: 10.1088/0031-9155/57/19/6245] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Sakama M, Kanai T, Fukumura A, Abe K. Evaluation ofwvalues for carbon beams in air, using a graphite calorimeter. Phys Med Biol 2009; 54:1111-30. [DOI: 10.1088/0031-9155/54/5/002] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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26
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de Prez LA, de Pooter JA. The new NMi orthovolt x-rays absorbed dose to water primary standard based on water calorimetry. Phys Med Biol 2008; 53:3531-42. [DOI: 10.1088/0031-9155/53/13/009] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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27
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Brede HJ, Greif KD, Hecker O, Heeg P, Heese J, Jones DTL, Kluge H, Schardt D. Absorbed dose to water determination with ionization chamber dosimetry and calorimetry in restricted neutron, photon, proton and heavy-ion radiation fields. Phys Med Biol 2006; 51:3667-82. [PMID: 16861773 DOI: 10.1088/0031-9155/51/15/005] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Absolute dose measurements with a transportable water calorimeter and ionization chambers were performed at a water depth of 20 mm in four different types of radiation fields, for a collimated (60)Co photon beam, for a collimated neutron beam with a fluence-averaged mean energy of 5.25 MeV, for collimated proton beams with mean energies of 36 MeV and 182 MeV at the measuring position, and for a (12)C ion beam in a scanned mode with an energy per atomic mass of 430 MeV u(-1). The ionization chambers actually used were calibrated in units of air kerma in the photon reference field of the PTB and in units of absorbed dose to water for a Farmer-type chamber at GSI. The absorbed dose to water inferred from calorimetry was compared with the dose derived from ionometry by applying the radiation-field-dependent parameters. For neutrons, the quantities of the ICRU Report 45, for protons the quantities of the ICRU Report 59 and for the (12)C ion beam, the recommended values of the International Atomic Energy Agency (IAEA) protocol (TRS 398) were applied. The mean values of the absolute absorbed dose to water obtained with these two independent methods agreed within the standard uncertainty (k = 1) of 1.8% for calorimetry and of 3.0% for ionometry for all types and energies of the radiation beams used in this comparison.
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Affiliation(s)
- H J Brede
- Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig,
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28
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Medin J, Ross CK, Klassen NV, Palmans H, Grusell E, Grindborg JE. Experimental determination of beam quality factors,kQ, for two types of Farmer chamber in a 10 MV photon and a 175 MeV proton beam. Phys Med Biol 2006; 51:1503-21. [PMID: 16510959 DOI: 10.1088/0031-9155/51/6/010] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Absorbed doses determined with a sealed water calorimeter operated at 4 degrees C are compared with the results obtained using ionization chambers and the IAEA TRS-398 code of practice in a 10 MV photon beam (TPR(20,10) = 0.734) and a 175 MeV proton beam (at a depth corresponding to the residual range, R(res) = 14.7 cm). Three NE 2571 and two FC65-G ionization chambers were calibrated in terms of absorbed-dose-to-water in (60)Co at the Swedish secondary standard dosimetry laboratory, directly traceable to the BIPM. In the photon beam quality, calorimetry was found to agree with ionometry within 0.3%, confirming the k(Q) values tabulated in TRS-398. In contrast, a 1.8% deviation was found in the proton beam at 6 g cm(-2) depth, suggesting that the TRS-398 tabulated k(Q) values for these two ionization chamber types are too high. Assuming no perturbation effect in the proton beam for the ionization chambers, a value for (w(air)/e)(Q) of 33.6 J C(-1) +/- 1.7% (k = 1) can be derived from these measurements. An analytical evaluation of the effect from non-elastic nuclear interactions in the ionization chamber wall indicates a perturbation effect of 0.6%. Including this estimated result in the proton beam would increase the determined (w(air)/e)(Q) value by the same amount.
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Affiliation(s)
- Joakim Medin
- Department of Medical Radiation Physics, Lund University, Malmö University Hospital, SE-205 02 Malmö, Sweden.
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29
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Abstract
Water calorimetry is considered to be the most direct primary method to realize the physical quantity gray for absorbed dose to water. The Swiss Federal Office of Metrology and Accreditation (METAS) has routinely operated a water calorimeter as primary standard for photon radiation since 2001. Nowadays, cancer therapy with proton radiation has become increasingly important and is a well established method. In the framework of the ProScan project conducted by the Paul Scherrer Institute (PSI), the spot-scanning technique is prepared for the subsequent application in hospitals, and adjusted to the recent findings of clinical research. In the absence of primary standards for proton radiation, the metrological traceability is assured by calibrating secondary standards in 60Co radiation and correcting with calculated beam quality correction factors. It is internationally recognized that the development of primary standards for proton radiation is highly desirable. In a common project of PSI and METAS, it is investigated whether a modified version of the water calorimeter in operation at METAS is suitable as primary standard for scanned proton radiation. A feasibility study has been conducted to investigate the linear energy transfer (LET) dependence of the heat defect and the influence of the time and space structure of the scanned beam on the homogeneity and stability of the temperature field in the water calorimeter. Simulations are validated against experimental data of the existing calorimeter used with photon radiation and extended to scanned proton radiation.
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Affiliation(s)
- M Sassowsky
- Swiss Federal Office of Metrology and Accreditation, Bern, Switzerland
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30
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Elbakri IA, Lakshminarayanan AV, Tesic MM. Automatic exposure control for a slot scanning full field digital mammography system. Med Phys 2005; 32:2763-70. [PMID: 16266089 DOI: 10.1118/1.1999107] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Automatic exposure control (AEC) is an important feature in mammography. It enables consistently optimal image exposure despite variations in tissue density and thickness, and user skill level. Full field digital mammography systems cannot employ conventional AEC methods because digital receptors fully absorb the x-ray beam. In this paper we describe an AEC procedure for slot scanning mammography. With slot scanning detectors, our approach uses a fast low-resolution and low-exposure prescan to acquire an image of the breast. Tube potential depends on breast thickness, and the prescan histogram provides the necessary information to calculate the required tube current. We validate our approach with simulated prescan images and phantom measurements. We achieve accurate exposure tracking with thickness and density, and expect this method of AEC to reduce retakes and improve workflow.
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Affiliation(s)
- Idris A Elbakri
- CancerCare Manitoba, 675 McDermot Ave, Winnipeg, MB R3W 0V9, Canada.
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31
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An experimental investigation of the electron energy dependence of the EPR alanine dosimetry system. RADIAT MEAS 2005. [DOI: 10.1016/j.radmeas.2004.05.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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32
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Bourhis-Martin E, Brede HJ, Greif KD, Baumhoer W, Rassow J, Sauerwein W. Absolute dosimetry in a d(14 MeV)+Be fast neutron beam. Med Phys 2004; 31:832-8. [PMID: 15125001 DOI: 10.1118/1.1668394] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Since 1978, the Universitätsklinikum in Essen operates a d(14 MeV) + Be fast neutron beam for patient treatment. Dosimetric studies were performed in a rectangular 40 x 40 mm2 neutron/photon field using a transportable water calorimeter, which had been developed at the Physikalisch-Technische Bundesanstalt. The water calorimeter allowed small dosimeters to be directly calibrated in units of absorbed dose-to-water in a cylindrical phantom of 50 mm in diameter. Also, the twin detector method was applied in order to determine the photon and the neutron dose separately. By making use of a calibrated ionization chamber, the absorbed dose-to-water calibration in the cylindrical water phantom was transferred to a water phantom, a cube 300 mm on a side. Experiments and Monte Carlo calculations covering the neutron producing target, the collimator and the influence of the water calorimeter on the spectral neutron fluence at the measurement position allow the relative uncertainty of the absorbed dose-to-water determination to be reduced to 2.6% (1 SD). This direct absorbed dose-to-water determination by calorimetry has shown that the treatment planning system underestimates the physical dose to tissue by 9%. For clinical purposes, the statement of the prescribed dose had to be increased by 9% in order that the absolute absorbed dose remains constant and that the same biological endpoints are reached.
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Affiliation(s)
- E Bourhis-Martin
- Strahlenklinik, Universitätsklinikum Essen, Hufelandstr. 55, 45122 Essen, Germany.
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33
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Huq MS, Andreo P. Advances in the determination of absorbed dose to water in clinical high-energy photon and electron beams using ionization chambers. Phys Med Biol 2004; 49:R49-104. [PMID: 15005158 DOI: 10.1088/0031-9155/49/4/r01] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
During the last two decades, absorbed dose to water in clinical photon and electron beams was determined using dosimetry protocols and codes of practice based on radiation metrology standards of air kerma. It is now recommended that clinical reference dosimetry be based on standards of absorbed dose to water. Newer protocols for the dosimetry of radiotherapy beams, based on the use of an ionization chamber calibrated in terms of absorbed dose to water, N(D,w), in a standards laboratory's reference quality beam, have been published by several national or regional scientific societies and international organizations. Since the publication of these protocols multiple theoretical and experimental dosimetry comparisons between the various N(D,w) based recommendations, and between the N(D,w) and the former air kerma (NK) based protocols, have been published. This paper provides a comprehensive review of the dosimetry protocols based on these standards and of the intercomparisons of the different protocols published in the literature, discussing the reasons for the observed discrepancies between them. A summary of the various types of standards of absorbed dose to water, together with an analysis of the uncertainties along the various steps of the dosimetry chain for the two types of formalism, is also included. It is emphasized that the NK-N(D,air) and N(D,w) formalisms have very similar uncertainty when the same criteria are used for both procedures. Arguments are provided in support of the recommendation for a change in reference dosimetry based on standards of absorbed dose to water.
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Affiliation(s)
- M Saiful Huq
- Department of Radiation Oncology, Kimmel Cancer Center of Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA
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34
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Vynckier S. Dosimetry of clinical neutron and proton beams: an overview of recommendations. RADIATION PROTECTION DOSIMETRY 2004; 110:565-572. [PMID: 15353710 DOI: 10.1093/rpd/nch221] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Neutron therapy beams are obtained by accelerating protons or deuterons on Beryllium. These neutron therapy beams present comparable dosimetric characteristics as those for photon beams obtained with linear accelerators; for instance, the penetration of a p(65)+Be neutron beam is comparable with the penetration of an 8 MV photon beam. In order to be competitive with conventional photon beam therapy, the dosimetric characteristics of the neutron beam should therefore not deviate too much from the photon beam characteristics. This paper presents a brief summary of the neutron beams used in radiotherapy. The dosimetry of the clinical neutron beams is described. Finally, recent and future developments in the field of physics for neutron therapy is mentioned. In the last two decades, a considerable number of centres have established radiotherapy treatment facilities using proton beams with energies between 50 and 250 MeV. Clinical applications require a relatively uniform dose to be delivered to the volume to be treated, and for this purpose the proton beam has to be spread out, both laterally and in depth. The technique is called 'beam modulation' and creates a region of high dose uniformity referred to as the 'spread-out Bragg peak'. Meanwhile, reference dosimetry in these beams had to catch up with photon and electron beams for which a much longer tradition of dosimetry exists. Proton beam dosimetry can be performed using different types of dosemeters, such as calorimeters, Faraday cups, track detectors and ionisation chambers. National standard dosimetry laboratories will, however, not provide a standard for the dosimetry of proton beams. To achieve uniformity on an international level, the use of an ionisation chamber should be considered. This paper reviews and summarises the basic principles and recommendations for the absorbed dose determination in a proton beam, utilising ionisation chambers calibrated in terms of absorbed dose to water. These recommendations are based on the recent IAEA TRS398 Code of Practice: 'Absorbed Dose Determination in External Beam Radiotherapy: An International Code of Practice for Dosimetry based on Standards of Absorbed Dose to Water'.
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Affiliation(s)
- S Vynckier
- Cliniques univ. St-Luc, Catholic University of Louvain, B-1200 Brussels, Belgium.
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35
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Reynolds JS, Troy TL, Mayer RH, Thompson AB, Waters DJ, Cornell KK, Snyder PW, Sevick-Muraca EM. Imaging of Spontaneous Canine Mammary Tumors Using Fluorescent Contrast Agents. Photochem Photobiol 1999. [DOI: 10.1111/j.1751-1097.1999.tb01953.x] [Citation(s) in RCA: 144] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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36
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Klassen NV, Shortt KR, Seuntjens J, Ross CK. Fricke dosimetry: the difference between G(Fe3+) for 60Co gamma-rays and high-energy x-rays. Phys Med Biol 1999; 44:1609-24. [PMID: 10442700 DOI: 10.1088/0031-9155/44/7/303] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
A calibration of the Fricke dosimeter is a measurement of epsilon G(Fe3+). Although G(Fe3+) is expected to be approximately energy independent for all low-LET radiation, existing data are not adequate to rule out the possibility of changes of a few per cent with beam quality. When a high-precision Fricke dosimeter, which has been calibrated for one particular low-LET beam quality, is used to measure the absorbed dose for another low-LET beam quality, the accuracy of the absorbed dose measurement is limited by the uncertainty in the value of G(Fe3+). The ratio of G(Fe3+) for high-energy x-rays (20 and 30 MV) to G(Fe3+) for 60Co gamma-rays, G(Fe3+)MV(Co), was measured to be 1.007(+/-0.003) (confidence level of 68%) using two different types of water calorimeter, a stirred-water calorimeter (20 MV) and a sealed-water calorimeter (20, 30 MV). This value is consistent with our calculations based on the LET dependence of G(primary products) and, as well, with published measurements and theoretical treatments of G(Fe3+).
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Affiliation(s)
- N V Klassen
- Ionizing Radiation Standards, Institute for National Measurement Standards, National Research Council, Ottawa, Ontario, Canada
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37
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Seuntjens J, Palmans H. Correction factors and performance of a 4 degrees C sealed water calorimeter. Phys Med Biol 1999; 44:627-46. [PMID: 10211799 DOI: 10.1088/0031-9155/44/3/001] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
In the past two decades, the water calorimetry technique for determination of absorbed dose to water in several types of radiation beams has moved significantly closer to being a recognized method. In this paper we summarize the constructional details of a 4 degrees C sealed water calorimeter currently in operation at the University of Gent. This sealed water (SW) calorimeter is of the Domen type and has been improved in several aspects compared with its original design. The relevant correction factors for heat transport and for field perturbation are described. Using relative response measurements in 60Co, we experimentally verified the relative heat defect for two distinct chemical systems, using two different detection vessel arrangements. The overall 1sigma uncertainty on the absorbed dose to water at 60Co based on this system amounts to 0.7%.
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Affiliation(s)
- J Seuntjens
- Department of Biomedical Physics, University of Gent, Belgium.
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38
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Farina B, Saponaro S, Pignoli E, Tomatis S, Marchesini R. Monte Carlo simulation of light fluence in tissue in a cylindrical diffusing fibre geometry. Phys Med Biol 1999; 44:1-11. [PMID: 10071871 DOI: 10.1088/0031-9155/44/1/002] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The propagation of light emitted by a linear light diffuser in a cylindrical hollow organ was investigated by means of the Monte Carlo (MC) method. The height and radius of the cavity, scattering (mu(s)) (or reduced scattering, mu'(s)) and absorption (mu(a)) coefficients, anisotropy (g), and refractive indices of the media involved (n1, n2) are required as input data by the MC code, as are characteristics of the light diffuser (length, delivered power and emission profile). Results of our MC model were tested by measuring the light fluence rate in a tissue-simulating phantom (mu(a) = 0.5 cm(-1), mu(s) = 23 cm(-1) and g = 0.75) irradiated at 633 nm with a cylindrical diffuser. Since geometric and optical parameters determine the behaviour of light propagation in tissue, MC simulations with different sets of input parameters were carried out to provide qualitative as well as quantitative data useful in planning photodynamic therapy. Data are reported on light penetration and fluence rate build-up at mu(a) and mu'(s) values ranging between 0.1 and 5 cm(-1) and 2.5 and 50 cm(-1), respectively. Furthermore, results suggest that a shift and spread could occur in the isofluence curves along the symmetry axis, which depend on the diameter of the treated lumen as well as on the emission profile of the light diffuser. Using our data it is possible to estimate how inaccuracy in knowledge of the optical coefficients can affect (i.e. usually by increasing) the light dose scheduled at a certain depth into tissue.
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Affiliation(s)
- B Farina
- Istituto Nazionale per lo Studio e la Cura dei Tumori, Milan, Italy
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39
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Huq MS, Yue N, Suntharalingam N. Experimental determination of fluence correction factors at depths beyond dmax for a Farmer type cylindrical ionization chamber in clinical electron beams. Med Phys 1997; 24:1609-13. [PMID: 9350714 DOI: 10.1118/1.597978] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Recently, it has been recommended that electron beam calibrations be performed at a new reference depth [Burns et al., Med. Phys. 23, 383 (1996)] given by dref = 0.6R50-0.1 cm, where R50 is the depth of 50% depth dose. In order to calibrate electron beams at dref with a Farmer type cylindrical ionization chamber, the values of the perturbation correction factors Pwall and Pfl at dref are required. Using a parallel plate Holt chamber as a reference chamber, the product PwallPfl has been determined for a 6.1-mm-diameter PTW cylindrical ionization chamber at dref as a function of R50 of clinical electron beams (6 < or = nominal energy E < or = 22 MeV). Assuming that Pwall for the PTW chamber is unity in electron beams, the measured Pfl values ranged from 0.96 to 0.98 as the energy is increased. These results are in close agreement with recently reported calculated values. Determination of dref requires the knowledge of R50. A relation between I50 and R50 is given in the IAEA Protocol [TRS No. 277 (IAEA, Vieńna, 1987), pp. 1-98] for broad beams at SSD = 100 cm. It has been shown experimentally that the equation R50 = 1.029 x I50-0.063 cm, derived by Ding et al. [Med. Phys. 22, 489 (1995)] from Monte Carlo simulations of realistic clinical electron beams, can be used satisfactorily to obtain R50 from I50, where I50 is the depth of 50% ionization. The largest difference between the measured value of R50 and that calculated by using the above equation has been found to be about 1 mm at 22 MeV.
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Affiliation(s)
- M S Huq
- Department of Radiation Oncology, Jefferson Medical College of Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
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