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Title: A virtual source model for Kilo-voltage cone beam CT: Source characteristics and model validation

Abstract

Purpose: The purpose of this investigation was to study the source characteristics of a clinical kilo-voltage cone beam CT unit and to develop and validate a virtual source model that could be used for treatment planning purposes. Methods: We used a previously commissioned full Monte Carlo model and new bespoke software to study the source characteristics of a clinical kilo-voltage cone beam CT (CBCT) unit. We identified the main particle sources, their spatial, energy and angular distribution for all the image acquisition presets currently used in our clinical practice. This includes a combination of two energies (100 and 120 kVp), two filters (neutral and bowtie), and eight different x-ray beam apertures. We subsequently built a virtual source model which we validated against full Monte Carlo calculations. Results: We found that the radiation output of the clinical kilo-voltage cone beam CT unit investigated in this study could be reproduced with a virtual model comprising of two sources (target and filtration cone) or three sources (target, filtration cone and bowtie filter) when additional filtration was used. With this model, we accounted for more than 97% of the photons exiting the unit. Each source in our model was characterised by a origin distributionmore » in both X and Y directions, a fluence map, a single energy spectrum for unfiltered beams and a two dimensional energy spectrum for bowtie filtered beams. The percentage dose difference between full Monte Carlo and virtual source model based dose distributions was well within the statistical uncertainty associated with the calculations ( {+-} 2%, one standard deviation) in all cases studied. Conclusions: The virtual source that we developed is accurate in calculating the dose delivered from a commercial kilo-voltage cone beam CT unit operating with routine clinical image acquisition settings. Our data have also shown that target, filtration cone, and bowtie filter sources needed to be all included in the model in order to accurately replicate the dose distribution from the clinical radiation beam.« less

Authors:
; ; ;  [1];  [2]
  1. Department of Medical Physics, Velindre Cancer Centre Cardiff CF14 2TL United Kingdom (United Kingdom)
  2. (Switzerland)
Publication Date:
OSTI Identifier:
22098625
Resource Type:
Journal Article
Journal Name:
Medical Physics
Additional Journal Information:
Journal Volume: 38; Journal Issue: 9; Other Information: (c) 2011 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0094-2405
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; 62 RADIOLOGY AND NUCLEAR MEDICINE; ANGULAR DISTRIBUTION; APERTURES; BEAMS; COMPUTER CODES; COMPUTERIZED TOMOGRAPHY; ENERGY SPECTRA; FILTERS; FILTRATION; IMAGE PROCESSING; MONTE CARLO METHOD; PARTICLE SOURCES; PHOTONS; RADIATION DOSE DISTRIBUTIONS; RADIATION DOSES; RADIOTHERAPY; TWO-DIMENSIONAL CALCULATIONS; X RADIATION

Citation Formats

Spezi, E., Volken, W., Frei, D., Fix, M. K., and Division of Medical Radiation Physics, Inselspital and University of Bern, CH-3010 Berne. A virtual source model for Kilo-voltage cone beam CT: Source characteristics and model validation. United States: N. p., 2011. Web. doi:10.1118/1.3626574.
Spezi, E., Volken, W., Frei, D., Fix, M. K., & Division of Medical Radiation Physics, Inselspital and University of Bern, CH-3010 Berne. A virtual source model for Kilo-voltage cone beam CT: Source characteristics and model validation. United States. doi:10.1118/1.3626574.
Spezi, E., Volken, W., Frei, D., Fix, M. K., and Division of Medical Radiation Physics, Inselspital and University of Bern, CH-3010 Berne. Thu . "A virtual source model for Kilo-voltage cone beam CT: Source characteristics and model validation". United States. doi:10.1118/1.3626574.
@article{osti_22098625,
title = {A virtual source model for Kilo-voltage cone beam CT: Source characteristics and model validation},
author = {Spezi, E. and Volken, W. and Frei, D. and Fix, M. K. and Division of Medical Radiation Physics, Inselspital and University of Bern, CH-3010 Berne},
abstractNote = {Purpose: The purpose of this investigation was to study the source characteristics of a clinical kilo-voltage cone beam CT unit and to develop and validate a virtual source model that could be used for treatment planning purposes. Methods: We used a previously commissioned full Monte Carlo model and new bespoke software to study the source characteristics of a clinical kilo-voltage cone beam CT (CBCT) unit. We identified the main particle sources, their spatial, energy and angular distribution for all the image acquisition presets currently used in our clinical practice. This includes a combination of two energies (100 and 120 kVp), two filters (neutral and bowtie), and eight different x-ray beam apertures. We subsequently built a virtual source model which we validated against full Monte Carlo calculations. Results: We found that the radiation output of the clinical kilo-voltage cone beam CT unit investigated in this study could be reproduced with a virtual model comprising of two sources (target and filtration cone) or three sources (target, filtration cone and bowtie filter) when additional filtration was used. With this model, we accounted for more than 97% of the photons exiting the unit. Each source in our model was characterised by a origin distribution in both X and Y directions, a fluence map, a single energy spectrum for unfiltered beams and a two dimensional energy spectrum for bowtie filtered beams. The percentage dose difference between full Monte Carlo and virtual source model based dose distributions was well within the statistical uncertainty associated with the calculations ( {+-} 2%, one standard deviation) in all cases studied. Conclusions: The virtual source that we developed is accurate in calculating the dose delivered from a commercial kilo-voltage cone beam CT unit operating with routine clinical image acquisition settings. Our data have also shown that target, filtration cone, and bowtie filter sources needed to be all included in the model in order to accurately replicate the dose distribution from the clinical radiation beam.},
doi = {10.1118/1.3626574},
journal = {Medical Physics},
issn = {0094-2405},
number = 9,
volume = 38,
place = {United States},
year = {2011},
month = {9}
}