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Title: SU-E-T-384: Experimental Verification of a Monte Carlo Linear Accelerator Model Using a Radiochromic Film Stack Dosimeter

Abstract

Purpose: To experimentally verify a Monte Carlo (MC) linear accelerator model for the simulation of intensity-modulated radiation therapy (IMRT) treatments of moving targets. Methods: A Varian Clinac™ 21EX linear accelerator was modeled using the EGSnrc user code BEAMnrc. The mean energy, radial-intensity distribution, and divergence of the electron beam incident on the bremsstrahlung target were adjusted to achieve agreement between simulated and measured percentage-depth-dose and transverse field profiles for a 6 MV beam. A seven-field step-and-shoot IMRT lung procedure was prepared using Varian Eclipse™ treatment planning software. The plan was delivered using a Clinac™ 21EX linear accelerator and measured with a Gafchromic™ EBT2 film stack dosimeter (FSD) in two separate static geometries: within a cylindrical water-equivalent-plastic phantom and within an anthropomorphic chest phantom. Two measurements were completed in each setup. The dose distribution for each geometry was simulated using the EGSnrc user code DOSXYZnrc. MC geometries of the treatment couch, cylindrical phantom, and chest phantom were developed by thresholding CT data sets using MATLAB™. The FSD was modeled as water. The measured and simulated dose distributions were normalized to the median dose within the FSD. Results: Using an electron beam with a mean energy of 6.05 MeV, a Gaussian radial-intensitymore » distribution with a full width at half maximum of 1.5 mm, and a divergence of 0°, the measured and simulated dose profiles agree within 1.75% and 1 mm. Measured and simulated dose distributions within both the cylindrical and chest phantoms agree within 3% over 94% of the FSD volume. The overall uncertainty in the FSD measurements is 3.1% (k=1). Conclusion: MC simulations agree with FSD measurements within measurement uncertainty, thereby verifying the accuracy of the linear accelerator model for the simulation of IMRT treatments of static geometries. The experimental verification will be extended to treatments of targets undergoing three-dimensional motion.« less

Authors:
; ;  [1]
  1. University of Wisconsin Medical Radiation Research Center, Madison, WI (United States)
Publication Date:
OSTI Identifier:
22355928
Resource Type:
Journal Article
Journal Name:
Medical Physics
Additional Journal Information:
Journal Volume: 41; Journal Issue: 6; Other Information: (c) 2014 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:
60 APPLIED LIFE SCIENCES; BREMSSTRAHLUNG; CHEST; DEPTH DOSE DISTRIBUTIONS; DOSEMETERS; ELECTRON BEAMS; GEOMETRY; LINEAR ACCELERATORS; LUNGS; MONTE CARLO METHOD; PHANTOMS; RADIATION DOSES; RADIOTHERAPY; SIMULATION

Citation Formats

McCaw, T, Culberson, W, and DeWerd, L. SU-E-T-384: Experimental Verification of a Monte Carlo Linear Accelerator Model Using a Radiochromic Film Stack Dosimeter. United States: N. p., 2014. Web. doi:10.1118/1.4888717.
McCaw, T, Culberson, W, & DeWerd, L. SU-E-T-384: Experimental Verification of a Monte Carlo Linear Accelerator Model Using a Radiochromic Film Stack Dosimeter. United States. https://doi.org/10.1118/1.4888717
McCaw, T, Culberson, W, and DeWerd, L. 2014. "SU-E-T-384: Experimental Verification of a Monte Carlo Linear Accelerator Model Using a Radiochromic Film Stack Dosimeter". United States. https://doi.org/10.1118/1.4888717.
@article{osti_22355928,
title = {SU-E-T-384: Experimental Verification of a Monte Carlo Linear Accelerator Model Using a Radiochromic Film Stack Dosimeter},
author = {McCaw, T and Culberson, W and DeWerd, L},
abstractNote = {Purpose: To experimentally verify a Monte Carlo (MC) linear accelerator model for the simulation of intensity-modulated radiation therapy (IMRT) treatments of moving targets. Methods: A Varian Clinac™ 21EX linear accelerator was modeled using the EGSnrc user code BEAMnrc. The mean energy, radial-intensity distribution, and divergence of the electron beam incident on the bremsstrahlung target were adjusted to achieve agreement between simulated and measured percentage-depth-dose and transverse field profiles for a 6 MV beam. A seven-field step-and-shoot IMRT lung procedure was prepared using Varian Eclipse™ treatment planning software. The plan was delivered using a Clinac™ 21EX linear accelerator and measured with a Gafchromic™ EBT2 film stack dosimeter (FSD) in two separate static geometries: within a cylindrical water-equivalent-plastic phantom and within an anthropomorphic chest phantom. Two measurements were completed in each setup. The dose distribution for each geometry was simulated using the EGSnrc user code DOSXYZnrc. MC geometries of the treatment couch, cylindrical phantom, and chest phantom were developed by thresholding CT data sets using MATLAB™. The FSD was modeled as water. The measured and simulated dose distributions were normalized to the median dose within the FSD. Results: Using an electron beam with a mean energy of 6.05 MeV, a Gaussian radial-intensity distribution with a full width at half maximum of 1.5 mm, and a divergence of 0°, the measured and simulated dose profiles agree within 1.75% and 1 mm. Measured and simulated dose distributions within both the cylindrical and chest phantoms agree within 3% over 94% of the FSD volume. The overall uncertainty in the FSD measurements is 3.1% (k=1). Conclusion: MC simulations agree with FSD measurements within measurement uncertainty, thereby verifying the accuracy of the linear accelerator model for the simulation of IMRT treatments of static geometries. The experimental verification will be extended to treatments of targets undergoing three-dimensional motion.},
doi = {10.1118/1.4888717},
url = {https://www.osti.gov/biblio/22355928}, journal = {Medical Physics},
issn = {0094-2405},
number = 6,
volume = 41,
place = {United States},
year = {Sun Jun 01 00:00:00 EDT 2014},
month = {Sun Jun 01 00:00:00 EDT 2014}
}