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Title: SU-E-T-775: Use of Electronic Portal Imaging Device (EPID) for Quality Assurance (QA) of Electron Beams On Varian Truebeam System

Abstract

Purpose: In a previous study we have demonstrated the feasibility of using EPID to QA electron beam parameters on a single Varian TrueBeam LINAC. This study aims to provide further investigation on (1) reproducibility of using EPID to detect electron beam energy changes on multiple machines and (2) evaluation of appropriate calibration methods to compare results from different EPIDs. Methods: Ad-hoc mode electron beam images were acquired in developer mode with XML code. Electron beam data were collected on a total of six machines from four institutions. A custom-designed double-wedge phantom was placed on the EPID detector. Two calibration methods - Pixel Sensitivity Map (PSM) and Large Source-to-Imager Distance Flood Field (LSID-FF) - were used. To test the sensitivity of EPID in detecting energy drifts, Bending Magnet Current (BMC) was detuned to invoke energy changes corresponding to ∼±1.5 mm change in R50% of PDD on two machines from two institutions. Percent depth ionization (PDI) curves were then analyzed and compared with the respective baseline images using LSID-FF calibration. For reproducibility testing, open field EPID images and images with a standard testing phantom were collected on multiple machines. Images with and without PSM correction for same energies on different machines weremore » overlaid and compared. Results: Two pixel shifts were observed in PDI curve when energy changes exceeded the TG142 tolerance. PSM showed the potential to correct the differences in pixel response of different imagers. With PSM correction, the histogram of images differences obtained from different machines showed narrower distributions than those images without PSM correction. Conclusion: EPID is sensitive for electron energy changes and the results are reproducible on different machines. When overlaying images from different machines, PSM showed the ability to partially eliminate the intrinsic variation of various imagers. Research Funding from Varian Medical Systems Inc.Dr. Sasa Mutic receives compensation for providing patient safety training services from Varian Medical Systems, the sponsor of this study.« less

Authors:
; ; ; ; ; ;  [1]
  1. Department of Radiation Oncology, Washington University in St Louis, St. Louis, MO (United States)
Publication Date:
OSTI Identifier:
22555142
Resource Type:
Journal Article
Journal Name:
Medical Physics
Additional Journal Information:
Journal Volume: 42; Journal Issue: 6; Other Information: (c) 2015 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; 61 RADIATION PROTECTION AND DOSIMETRY; BIOMEDICAL RADIOGRAPHY; CALIBRATION; CORRECTIONS; DIAGRAMS; ELECTRON BEAMS; IMAGES; LINEAR ACCELERATORS; PHANTOMS; QUALITY ASSURANCE

Citation Formats

Cai, B, Yaddanapudi, S, Sun, B, Li, H, Noel, C, Mutic, S, and Goddu, S. SU-E-T-775: Use of Electronic Portal Imaging Device (EPID) for Quality Assurance (QA) of Electron Beams On Varian Truebeam System. United States: N. p., 2015. Web. doi:10.1118/1.4925139.
Cai, B, Yaddanapudi, S, Sun, B, Li, H, Noel, C, Mutic, S, & Goddu, S. SU-E-T-775: Use of Electronic Portal Imaging Device (EPID) for Quality Assurance (QA) of Electron Beams On Varian Truebeam System. United States. https://doi.org/10.1118/1.4925139
Cai, B, Yaddanapudi, S, Sun, B, Li, H, Noel, C, Mutic, S, and Goddu, S. 2015. "SU-E-T-775: Use of Electronic Portal Imaging Device (EPID) for Quality Assurance (QA) of Electron Beams On Varian Truebeam System". United States. https://doi.org/10.1118/1.4925139.
@article{osti_22555142,
title = {SU-E-T-775: Use of Electronic Portal Imaging Device (EPID) for Quality Assurance (QA) of Electron Beams On Varian Truebeam System},
author = {Cai, B and Yaddanapudi, S and Sun, B and Li, H and Noel, C and Mutic, S and Goddu, S},
abstractNote = {Purpose: In a previous study we have demonstrated the feasibility of using EPID to QA electron beam parameters on a single Varian TrueBeam LINAC. This study aims to provide further investigation on (1) reproducibility of using EPID to detect electron beam energy changes on multiple machines and (2) evaluation of appropriate calibration methods to compare results from different EPIDs. Methods: Ad-hoc mode electron beam images were acquired in developer mode with XML code. Electron beam data were collected on a total of six machines from four institutions. A custom-designed double-wedge phantom was placed on the EPID detector. Two calibration methods - Pixel Sensitivity Map (PSM) and Large Source-to-Imager Distance Flood Field (LSID-FF) - were used. To test the sensitivity of EPID in detecting energy drifts, Bending Magnet Current (BMC) was detuned to invoke energy changes corresponding to ∼±1.5 mm change in R50% of PDD on two machines from two institutions. Percent depth ionization (PDI) curves were then analyzed and compared with the respective baseline images using LSID-FF calibration. For reproducibility testing, open field EPID images and images with a standard testing phantom were collected on multiple machines. Images with and without PSM correction for same energies on different machines were overlaid and compared. Results: Two pixel shifts were observed in PDI curve when energy changes exceeded the TG142 tolerance. PSM showed the potential to correct the differences in pixel response of different imagers. With PSM correction, the histogram of images differences obtained from different machines showed narrower distributions than those images without PSM correction. Conclusion: EPID is sensitive for electron energy changes and the results are reproducible on different machines. When overlaying images from different machines, PSM showed the ability to partially eliminate the intrinsic variation of various imagers. Research Funding from Varian Medical Systems Inc.Dr. Sasa Mutic receives compensation for providing patient safety training services from Varian Medical Systems, the sponsor of this study.},
doi = {10.1118/1.4925139},
url = {https://www.osti.gov/biblio/22555142}, journal = {Medical Physics},
issn = {0094-2405},
number = 6,
volume = 42,
place = {United States},
year = {Mon Jun 15 00:00:00 EDT 2015},
month = {Mon Jun 15 00:00:00 EDT 2015}
}