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J J W Lagendijk - One of the best experts on this subject based on the ideXlab platform.
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towards reference dosimetry for the mr linac magnetic field correction of the Ionization Chamber reading
Physics in Medicine and Biology, 2013Co-Authors: K Smit, B Van Asselen, J G M Kok, A H L Aalbers, J J W Lagendijk, B W RaaymakersAbstract:In the UMC Utrecht a prototype MR-linac has been installed. The system consists of a 6 MV Elekta (Crawley, UK) linear accelerator and a 1.5 T Philips (Best, The Netherlands) Achieva MRI system. This paper investigates the feasibility to correct the Ionization Chamber reading for the magnetic field within the dosimetry calibration method described by Almond et al (1999 Med. Phys. 26 1847–70). Firstly, the feasibility of using an Ionization Chamber in an MR-linac was assessed by investigating possible influences of the magnetic field on NE2571 Farmer-type Ionization Chamber characteristics: linearity, repeatability, orientation in the magnetic field; and AAPM TG51 correction factor for voltage polarity and ion recombination. We found that these AAPM correction factors for the NE2571 Chamber were not influenced by the magnetic field. Secondly, the influence of the permanent 1.5 T magnetic field on the NE2571 Chamber reading was quantified. The reading is influenced by the magnetic field; therefore, a correction factor has been added. For the standardized setup used in this paper, the NE2571 Chamber reading increases by 4.9% (± 0.2%) due to the transverse 1.5 T magnetic field. Dosimetry measurements in an MR-linac are feasible, if a setup-specific magnetic field correction factor (P1.5 T) for the charge reading is introduced. For the setup investigated in this paper, the P1.5 T has a value of 0.953.
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dosimetry for the mri accelerator the impact of a magnetic field on the response of a farmer ne2571 Ionization Chamber
Physics in Medicine and Biology, 2009Co-Authors: I Meijsing, B W Raaymakers, Aje Raaijmakers, J W Kok, L Hogeweg, Bo B Liu, J J W LagendijkAbstract:The UMC Utrecht is constructing a 1.5 T MRI scanner integrated with a linear accelerator (Lagendijk et al 2008 Radiother. Oncol. 86 25?9). The goal of this device is to facilitate soft-tissue contrast based image-guided radiotherapy, in order to escalate the dose to the tumour while sparing surrounding normal tissues. Dosimetry for the MRI accelerator has to be performed in the presence of a magnetic field. This paper investigates the feasibility of using a Farmer NE2571 Ionization Chamber for absolute dosimetry. The impact of the magnetic field on the response of this Ionization Chamber has been measured and simulated using Monte Carlo simulations. Two orientations of the Ionization Chamber with respect to the incident beam and the magnetic field which are feasible in the MRI accelerator configuration are taken into account. Measurements are performed using a laboratory magnet ranging from 0 to 1.2 T. In the simulations a range from 0 to 2 T is used. For both orientations, the measurements and simulations agreed within the uncertainty of the measurements and simulations. In conclusion, the response of the Ionization Chamber as a function of the magnetic field is understood and can be simulated using Monte Carlo simulations.
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dosimetry for the mri accelerator the impact of a magnetic field on the response of a farmer ne2571 Ionization Chamber
Physics in Medicine and Biology, 2009Co-Authors: I Meijsing, B W Raaymakers, Aje Raaijmakers, J W Kok, L Hogeweg, Bo B Liu, J J W LagendijkAbstract:The UMC Utrecht is constructing a 1.5 T MRI scanner integrated with a linear accelerator (Lagendijk et al 2008 Radiother. Oncol. 86 25-9). The goal of this device is to facilitate soft-tissue contrast based image-guided radiotherapy, in order to escalate the dose to the tumour while sparing surrounding normal tissues. Dosimetry for the MRI accelerator has to be performed in the presence of a magnetic field. This paper investigates the feasibility of using a Farmer NE2571 Ionization Chamber for absolute dosimetry. The impact of the mcagnetic field on the response of this Ionization Chamber has been measured and simulated using GEANT4 Monte Carlo simulations. Two orientations of the Ionization Chamber with respect to the incident beam and the magnetic field which are feasible in the MRI accelerator configuration are taken into account. Measurements are performed using a laboratory magnet ranging from 0 to 1.2 T. In the simulations a range from 0 to 2 T is used. For both orientations, the measurements and simulations agreed within the uncertainty of the measurements and simulations. In conclusion, the response of the Ionization Chamber as a function of the magnetic field is understood and can be simulated using GEANT4 Monte Carlo simulations.
B W Raaymakers - One of the best experts on this subject based on the ideXlab platform.
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towards reference dosimetry for the mr linac magnetic field correction of the Ionization Chamber reading
Physics in Medicine and Biology, 2013Co-Authors: K Smit, B Van Asselen, J G M Kok, A H L Aalbers, J J W Lagendijk, B W RaaymakersAbstract:In the UMC Utrecht a prototype MR-linac has been installed. The system consists of a 6 MV Elekta (Crawley, UK) linear accelerator and a 1.5 T Philips (Best, The Netherlands) Achieva MRI system. This paper investigates the feasibility to correct the Ionization Chamber reading for the magnetic field within the dosimetry calibration method described by Almond et al (1999 Med. Phys. 26 1847–70). Firstly, the feasibility of using an Ionization Chamber in an MR-linac was assessed by investigating possible influences of the magnetic field on NE2571 Farmer-type Ionization Chamber characteristics: linearity, repeatability, orientation in the magnetic field; and AAPM TG51 correction factor for voltage polarity and ion recombination. We found that these AAPM correction factors for the NE2571 Chamber were not influenced by the magnetic field. Secondly, the influence of the permanent 1.5 T magnetic field on the NE2571 Chamber reading was quantified. The reading is influenced by the magnetic field; therefore, a correction factor has been added. For the standardized setup used in this paper, the NE2571 Chamber reading increases by 4.9% (± 0.2%) due to the transverse 1.5 T magnetic field. Dosimetry measurements in an MR-linac are feasible, if a setup-specific magnetic field correction factor (P1.5 T) for the charge reading is introduced. For the setup investigated in this paper, the P1.5 T has a value of 0.953.
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dosimetry for the mri accelerator the impact of a magnetic field on the response of a farmer ne2571 Ionization Chamber
Physics in Medicine and Biology, 2009Co-Authors: I Meijsing, B W Raaymakers, Aje Raaijmakers, J W Kok, L Hogeweg, Bo B Liu, J J W LagendijkAbstract:The UMC Utrecht is constructing a 1.5 T MRI scanner integrated with a linear accelerator (Lagendijk et al 2008 Radiother. Oncol. 86 25?9). The goal of this device is to facilitate soft-tissue contrast based image-guided radiotherapy, in order to escalate the dose to the tumour while sparing surrounding normal tissues. Dosimetry for the MRI accelerator has to be performed in the presence of a magnetic field. This paper investigates the feasibility of using a Farmer NE2571 Ionization Chamber for absolute dosimetry. The impact of the magnetic field on the response of this Ionization Chamber has been measured and simulated using Monte Carlo simulations. Two orientations of the Ionization Chamber with respect to the incident beam and the magnetic field which are feasible in the MRI accelerator configuration are taken into account. Measurements are performed using a laboratory magnet ranging from 0 to 1.2 T. In the simulations a range from 0 to 2 T is used. For both orientations, the measurements and simulations agreed within the uncertainty of the measurements and simulations. In conclusion, the response of the Ionization Chamber as a function of the magnetic field is understood and can be simulated using Monte Carlo simulations.
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dosimetry for the mri accelerator the impact of a magnetic field on the response of a farmer ne2571 Ionization Chamber
Physics in Medicine and Biology, 2009Co-Authors: I Meijsing, B W Raaymakers, Aje Raaijmakers, J W Kok, L Hogeweg, Bo B Liu, J J W LagendijkAbstract:The UMC Utrecht is constructing a 1.5 T MRI scanner integrated with a linear accelerator (Lagendijk et al 2008 Radiother. Oncol. 86 25-9). The goal of this device is to facilitate soft-tissue contrast based image-guided radiotherapy, in order to escalate the dose to the tumour while sparing surrounding normal tissues. Dosimetry for the MRI accelerator has to be performed in the presence of a magnetic field. This paper investigates the feasibility of using a Farmer NE2571 Ionization Chamber for absolute dosimetry. The impact of the mcagnetic field on the response of this Ionization Chamber has been measured and simulated using GEANT4 Monte Carlo simulations. Two orientations of the Ionization Chamber with respect to the incident beam and the magnetic field which are feasible in the MRI accelerator configuration are taken into account. Measurements are performed using a laboratory magnet ranging from 0 to 1.2 T. In the simulations a range from 0 to 2 T is used. For both orientations, the measurements and simulations agreed within the uncertainty of the measurements and simulations. In conclusion, the response of the Ionization Chamber as a function of the magnetic field is understood and can be simulated using GEANT4 Monte Carlo simulations.
J J Battista - One of the best experts on this subject based on the ideXlab platform.
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response to comments on Ionization Chamber volume determination and quality assurance using micro ct imaging
Physics in Medicine and Biology, 2009Co-Authors: A Mcniven, J Umoh, Tomas Kron, David W Holdsworth, J J BattistaAbstract:Air Ionization Chamber dosimetry plays a crucial role in international dose calibration for the radiotherapy clinical environment. Micro-CT images of ion Chambers can play an important role in quality assurance of these devices by detecting internal geometry, materials and defects non-invasively, as we demonstrated (McNiven et al 2008 Phys. Med. Biol. 53 5029–43). We also suggested that electric-field simulation based upon these accurate Chamber-specific 3D images rather than manufacturer blueprints could be valuable in assessing ionometric sensitivity. As recently performed by Ross et al these electric field simulations play a vital role in understanding key components that contribute to the Chamber sensitive volume and Ionization calibration coefficients.
A Lourenco - One of the best experts on this subject based on the ideXlab platform.
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the influence of nuclear interactions on Ionization Chamber perturbation factors in proton beams fluka simulations supported by a fano test
Medical Physics, 2019Co-Authors: Hugo Bouchard, A Lourenco, S Galer, G J Royle, H PalmansAbstract:PURPOSE: In all recent protocols for the reference dosimetry of clinical proton beams Ionization Chamber perturbation factors are assumed to be unity. In this work, such factors were computed using the FLUKA Monte Carlo code for three Ionization Chamber types, with particular attention to the influence of nuclear interactions. METHODS: The accuracy of the transport algorithms implemented in FLUKA was first evaluated by performing a Fano cavity test. Ionization Chamber perturbation factors were computed for the PTW-34001 Roos® and the PTW-34070 and PTW-34073 Bragg peak® Chambers for proton beams of 60 to 250 MeV using the same transport parameters that were needed to pass the Fano test. RESULTS: FLUKA was found to pass the Fano test within 0.15%. Ionization Chamber simulation results show that the presence of the air cavity and the wall results in dose perturbations of the order of 0.6% and 0.8%, respectively. The perturbation factors are shown to be energy dependent and nuclear interactions must be taken into account for accurate calculation of the Ionization Chamber's response. CONCLUSION: Ionization Chamber perturbations can amount to 1% in high-energy proton beams and therefore need to be considered in dosimetry procedures. This article is protected by copyright. All rights reserved.
K H Shin - One of the best experts on this subject based on the ideXlab platform.
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a well type Ionization Chamber geometric correction factor
Physics in Medicine and Biology, 1996Co-Authors: R J Meiler, C H Sibata, C N De Souza, K H ShinAbstract:To correct for the influence of source configuration on the measured activity of spherical and cylindrical brachytherapy sources, a geometric correction factor was calculated for the Standard Imaging HDR-1000 well-type Ionization Chamber. A Fortran program modelled each source as a lattice of point sources. Because of the cylindrical symmetry of the well Chamber, it could be uniquely modelled by point detectors along the perimeter of the radial plane of the detection volume. Path lengths were calculated and attenuation factors were applied to each source - detector point combination individually. The total dose rate at each detection point was found through a Sievert summation of the point source contributions. For sources with identical activities, a correction factor of was calculated, equal to the ratio of the dose rate of the cylindrical source to that of the sphere. Experimental verification using a Nuclear Associates 67-809 series cylindrical source and an Amersham spherical source yielded a correction factor of .
