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Title: Monte Carlo modelling of a-Si EPID response: The effect of spectral variations with field size and position

Abstract

This study focused on predicting the electronic portal imaging device (EPID) image of intensity modulated radiation treatment (IMRT) fields in the absence of attenuation material in the beam with Monte Carlo methods. As IMRT treatments consist of a series of segments of various sizes that are not always delivered on the central axis, large spectral variations may be observed between the segments. The effect of these spectral variations on the EPID response was studied with fields of various sizes and off-axis positions. A detailed description of the EPID was implemented in a Monte Carlo model. The EPID model was validated by comparing the EPID output factors for field sizes between 1x1 and 26x26 cm{sup 2} at the isocenter. The Monte Carlo simulations agreed with the measurements to within 1.5%. The Monte Carlo model succeeded in predicting the EPID response at the center of the fields of various sizes and offsets to within 1% of the measurements. Large variations (up to 29%) of the EPID response were observed between the various offsets. The EPID response increased with field size and with field offset for most cases. The Monte Carlo model was then used to predict the image of a simple testmore » IMRT field delivered on the beam axis and with an offset. A variation of EPID response up to 28% was found between the on- and off-axis delivery. Finally, two clinical IMRT fields were simulated and compared to the measurements. For all IMRT fields, simulations and measurements agreed within 3%--0.2 cm for 98% of the pixels. The spectral variations were quantified by extracting from the spectra at the center of the fields the total photon yield (Y{sub total}), the photon yield below 1 MeV (Y{sub low}), and the percentage of photons below 1 MeV (P{sub low}). For the studied cases, a correlation was shown between the EPID response variation and Y{sub total}, Y{sub low}, and P{sub low}.« less

Authors:
; ; ; ;  [1]
  1. Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Downs Road, Sutton, SM2 5PT (United Kingdom)
Publication Date:
OSTI Identifier:
20853820
Resource Type:
Journal Article
Journal Name:
Medical Physics
Additional Journal Information:
Journal Volume: 33; Journal Issue: 12; Other Information: DOI: 10.1118/1.2369465; (c) 2006 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:
62 RADIOLOGY AND NUCLEAR MEDICINE; ATTENUATION; BEAMS; COMPUTERIZED SIMULATION; DOSIMETRY; IMAGES; MODULATION; MONTE CARLO METHOD; PHOTONS; RADIOTHERAPY; SILICON; SPECTRA

Citation Formats

Parent, Laure, Seco, Joao, Evans, Phil M, Fielding, Andrew, Dance, David R, School of Physical and Chemical Sciences, Queensland University of Technology, Q337 Gardens Point Campus, Brisbane, Queensland 4001, and Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Fulham Road, London, SW3 6JJ. Monte Carlo modelling of a-Si EPID response: The effect of spectral variations with field size and position. United States: N. p., 2006. Web. doi:10.1118/1.2369465.
Parent, Laure, Seco, Joao, Evans, Phil M, Fielding, Andrew, Dance, David R, School of Physical and Chemical Sciences, Queensland University of Technology, Q337 Gardens Point Campus, Brisbane, Queensland 4001, & Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Fulham Road, London, SW3 6JJ. Monte Carlo modelling of a-Si EPID response: The effect of spectral variations with field size and position. United States. https://doi.org/10.1118/1.2369465
Parent, Laure, Seco, Joao, Evans, Phil M, Fielding, Andrew, Dance, David R, School of Physical and Chemical Sciences, Queensland University of Technology, Q337 Gardens Point Campus, Brisbane, Queensland 4001, and Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Fulham Road, London, SW3 6JJ. 2006. "Monte Carlo modelling of a-Si EPID response: The effect of spectral variations with field size and position". United States. https://doi.org/10.1118/1.2369465.
@article{osti_20853820,
title = {Monte Carlo modelling of a-Si EPID response: The effect of spectral variations with field size and position},
author = {Parent, Laure and Seco, Joao and Evans, Phil M and Fielding, Andrew and Dance, David R and School of Physical and Chemical Sciences, Queensland University of Technology, Q337 Gardens Point Campus, Brisbane, Queensland 4001 and Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Fulham Road, London, SW3 6JJ},
abstractNote = {This study focused on predicting the electronic portal imaging device (EPID) image of intensity modulated radiation treatment (IMRT) fields in the absence of attenuation material in the beam with Monte Carlo methods. As IMRT treatments consist of a series of segments of various sizes that are not always delivered on the central axis, large spectral variations may be observed between the segments. The effect of these spectral variations on the EPID response was studied with fields of various sizes and off-axis positions. A detailed description of the EPID was implemented in a Monte Carlo model. The EPID model was validated by comparing the EPID output factors for field sizes between 1x1 and 26x26 cm{sup 2} at the isocenter. The Monte Carlo simulations agreed with the measurements to within 1.5%. The Monte Carlo model succeeded in predicting the EPID response at the center of the fields of various sizes and offsets to within 1% of the measurements. Large variations (up to 29%) of the EPID response were observed between the various offsets. The EPID response increased with field size and with field offset for most cases. The Monte Carlo model was then used to predict the image of a simple test IMRT field delivered on the beam axis and with an offset. A variation of EPID response up to 28% was found between the on- and off-axis delivery. Finally, two clinical IMRT fields were simulated and compared to the measurements. For all IMRT fields, simulations and measurements agreed within 3%--0.2 cm for 98% of the pixels. The spectral variations were quantified by extracting from the spectra at the center of the fields the total photon yield (Y{sub total}), the photon yield below 1 MeV (Y{sub low}), and the percentage of photons below 1 MeV (P{sub low}). For the studied cases, a correlation was shown between the EPID response variation and Y{sub total}, Y{sub low}, and P{sub low}.},
doi = {10.1118/1.2369465},
url = {https://www.osti.gov/biblio/20853820}, journal = {Medical Physics},
issn = {0094-2405},
number = 12,
volume = 33,
place = {United States},
year = {Fri Dec 15 00:00:00 EST 2006},
month = {Fri Dec 15 00:00:00 EST 2006}
}