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Title: Improvement of Varian a-Si EPID dosimetry measurements using a lead-shielded support-arm

Abstract

Dosimetry measurements with Varian amorphous silicon electronic portal imaging devices (a-Si EPIDs) are affected by the backscattered radiation from the EPID support arm. In this study, the nonuniform backscatter from an E-type support arm was reduced by fixing a thick (12.2 Multiplication-Sign 10.5 Multiplication-Sign 0.5 cm{sup 3}) piece of lead on top of the arm, and the remaining backscatter was modeled and included in an existing dose prediction algorithm. The applied backscatter kernel was the average of kernels on different regions of the EPID over the arm. The lead-shielded arm reduced the nonuniform backscatter component by about 50% for field sizes ranging from 3 Multiplication-Sign 3 to 30 Multiplication-Sign 30 cm{sup 2} and the field symmetry improved for medium to large fields up to 3%. Gamma evaluation of the measured and modeled doses (2%, 2-mm criteria) showed that using the lead-shielded arm in the model increased the number of points with Gamma index <1 by 5.7% and decreased the mean Gamma by 0.201. Even using the lead alone (no modeling) could increase the number of points with Gamma index <1 by 4.7% and decrease the mean Gamma by 0.153. This is a simple and easy method to decrease the nonuniformmore » arm backscatter and improve the accuracy of dosimetry measurements with the existing EPIDs used for clinical applications.« less

Authors:
 [1]; ;  [1];  [1]
  1. School of Mathematical and Physical Sciences, University of Newcastle, Newcastle, New South Wales (Australia)
Publication Date:
OSTI Identifier:
22130395
Resource Type:
Journal Article
Journal Name:
Medical Dosimetry
Additional Journal Information:
Journal Volume: 37; Journal Issue: 2; Other Information: Copyright (c) 2012 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0958-3947
Country of Publication:
United States
Language:
English
Subject:
61 RADIATION PROTECTION AND DOSIMETRY; ACCURACY; ALGORITHMS; DOSIMETRY; EVALUATION; FORECASTING; KERNELS; LEAD; RADIATION DOSES; SHIELDING; SILICON; SIMULATION; SYMMETRY

Citation Formats

Rowshanfarzad, Pejman, Sabet, Mahsheed, O'Connor, Daryl J., Greer, Peter B., and Department of Radiation Oncology, Calvary Mater Newcastle Hospital, Newcastle, New South Wales. Improvement of Varian a-Si EPID dosimetry measurements using a lead-shielded support-arm. United States: N. p., 2012. Web. doi:10.1016/J.MEDDOS.2011.06.003.
Rowshanfarzad, Pejman, Sabet, Mahsheed, O'Connor, Daryl J., Greer, Peter B., & Department of Radiation Oncology, Calvary Mater Newcastle Hospital, Newcastle, New South Wales. Improvement of Varian a-Si EPID dosimetry measurements using a lead-shielded support-arm. United States. https://doi.org/10.1016/J.MEDDOS.2011.06.003
Rowshanfarzad, Pejman, Sabet, Mahsheed, O'Connor, Daryl J., Greer, Peter B., and Department of Radiation Oncology, Calvary Mater Newcastle Hospital, Newcastle, New South Wales. 2012. "Improvement of Varian a-Si EPID dosimetry measurements using a lead-shielded support-arm". United States. https://doi.org/10.1016/J.MEDDOS.2011.06.003.
@article{osti_22130395,
title = {Improvement of Varian a-Si EPID dosimetry measurements using a lead-shielded support-arm},
author = {Rowshanfarzad, Pejman and Sabet, Mahsheed and O'Connor, Daryl J. and Greer, Peter B. and Department of Radiation Oncology, Calvary Mater Newcastle Hospital, Newcastle, New South Wales},
abstractNote = {Dosimetry measurements with Varian amorphous silicon electronic portal imaging devices (a-Si EPIDs) are affected by the backscattered radiation from the EPID support arm. In this study, the nonuniform backscatter from an E-type support arm was reduced by fixing a thick (12.2 Multiplication-Sign 10.5 Multiplication-Sign 0.5 cm{sup 3}) piece of lead on top of the arm, and the remaining backscatter was modeled and included in an existing dose prediction algorithm. The applied backscatter kernel was the average of kernels on different regions of the EPID over the arm. The lead-shielded arm reduced the nonuniform backscatter component by about 50% for field sizes ranging from 3 Multiplication-Sign 3 to 30 Multiplication-Sign 30 cm{sup 2} and the field symmetry improved for medium to large fields up to 3%. Gamma evaluation of the measured and modeled doses (2%, 2-mm criteria) showed that using the lead-shielded arm in the model increased the number of points with Gamma index <1 by 5.7% and decreased the mean Gamma by 0.201. Even using the lead alone (no modeling) could increase the number of points with Gamma index <1 by 4.7% and decrease the mean Gamma by 0.153. This is a simple and easy method to decrease the nonuniform arm backscatter and improve the accuracy of dosimetry measurements with the existing EPIDs used for clinical applications.},
doi = {10.1016/J.MEDDOS.2011.06.003},
url = {https://www.osti.gov/biblio/22130395}, journal = {Medical Dosimetry},
issn = {0958-3947},
number = 2,
volume = 37,
place = {United States},
year = {Sun Jul 01 00:00:00 EDT 2012},
month = {Sun Jul 01 00:00:00 EDT 2012}
}