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Title: SU-E-T-128: Dosimetric Evaluation of MLC Modeling in Pinnacle V9.2 for Varian TrueBeam STx

Abstract

Purpose: To evaluate the effects of MLC modeling after commissioning the Varian TrueBeam LINAC in Pinnacle version 9.2. Methods: Stepand-shoot IMRT QAs were investigated when we observed our measured absolute dose results using ion chamber (Capintec PR-05P) were uncharacteristically low; about 4–5% compared to doses calculated by Pinnacle{sup 3} (Phillips, Madison, WI). This problem was predominant for large and highly modulated head and neck (HN) treatments. Intuitively we knew this had to be related to shortcomings in the MLC modeling in Pinnacle. Using film QA we were able to iteratively adjust the MLC parameters. We confirmed results by re-testing five failed IMRT QA patients; and ion chamber measurements were verified in Quasar anthropomorphic phantom. Results: After commissioning the LINAC in Pinnacle version 9.2, the MLC transmission for 6X, 10X and 15X were 2.0%, 1.7% and 2.0%, respectively, and additional Interleaf leakage for all three energies was 0.5%. These parameters were obtained from profiles scanned with an Edge detector (Sun Nuclear, Melbourne, FL) during machine commissioning. A Verification testing with radiographic EDR2 film (Kodak, Rochester, NY) measurement was performed by creating a closed MLC leaf pattern and analyzing using RIT software (RIT, Colorado Springs, CO). This reduced MLC transmission for 6X,more » 10X and 15X to 0.7%, 0.9% and 0.9%, respectively; while increasing additional Interleaf leakage for all three energies to 1.0%. Conclusion: Radiographic film measurements were used to correct MLC transmission values for step and shoot IMRT fields used in Pinnacle version 9.2. After adjusting the MLC parameters to correlate with the film QA, there was still very good agreement between the Pinnacle model and commissioning data. Using the same QA methodology, we were also able to improve the beam models for the Varian C-series linacs, Novalis-Tx, and TrueBeam M-120 linacs.« less

Authors:
; ; ;  [1]
  1. CARTI, Inc., Little Rock, AR (United States)
Publication Date:
OSTI Identifier:
22339882
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:
07 ISOTOPES AND RADIATION SOURCES; 60 APPLIED LIFE SCIENCES; CARBON MONOXIDE; COMMISSIONING; COMPUTER CODES; FILM DOSIMETRY; IONIZATION CHAMBERS; ITERATIVE METHODS; LINEAR ACCELERATORS; PHANTOMS; RADIATION DOSES; SIMULATION

Citation Formats

Otageri, P, Grant, E, Maricle, S, and Mathews, B. SU-E-T-128: Dosimetric Evaluation of MLC Modeling in Pinnacle V9.2 for Varian TrueBeam STx. United States: N. p., 2014. Web. doi:10.1118/1.4888458.
Otageri, P, Grant, E, Maricle, S, & Mathews, B. SU-E-T-128: Dosimetric Evaluation of MLC Modeling in Pinnacle V9.2 for Varian TrueBeam STx. United States. https://doi.org/10.1118/1.4888458
Otageri, P, Grant, E, Maricle, S, and Mathews, B. 2014. "SU-E-T-128: Dosimetric Evaluation of MLC Modeling in Pinnacle V9.2 for Varian TrueBeam STx". United States. https://doi.org/10.1118/1.4888458.
@article{osti_22339882,
title = {SU-E-T-128: Dosimetric Evaluation of MLC Modeling in Pinnacle V9.2 for Varian TrueBeam STx},
author = {Otageri, P and Grant, E and Maricle, S and Mathews, B},
abstractNote = {Purpose: To evaluate the effects of MLC modeling after commissioning the Varian TrueBeam LINAC in Pinnacle version 9.2. Methods: Stepand-shoot IMRT QAs were investigated when we observed our measured absolute dose results using ion chamber (Capintec PR-05P) were uncharacteristically low; about 4–5% compared to doses calculated by Pinnacle{sup 3} (Phillips, Madison, WI). This problem was predominant for large and highly modulated head and neck (HN) treatments. Intuitively we knew this had to be related to shortcomings in the MLC modeling in Pinnacle. Using film QA we were able to iteratively adjust the MLC parameters. We confirmed results by re-testing five failed IMRT QA patients; and ion chamber measurements were verified in Quasar anthropomorphic phantom. Results: After commissioning the LINAC in Pinnacle version 9.2, the MLC transmission for 6X, 10X and 15X were 2.0%, 1.7% and 2.0%, respectively, and additional Interleaf leakage for all three energies was 0.5%. These parameters were obtained from profiles scanned with an Edge detector (Sun Nuclear, Melbourne, FL) during machine commissioning. A Verification testing with radiographic EDR2 film (Kodak, Rochester, NY) measurement was performed by creating a closed MLC leaf pattern and analyzing using RIT software (RIT, Colorado Springs, CO). This reduced MLC transmission for 6X, 10X and 15X to 0.7%, 0.9% and 0.9%, respectively; while increasing additional Interleaf leakage for all three energies to 1.0%. Conclusion: Radiographic film measurements were used to correct MLC transmission values for step and shoot IMRT fields used in Pinnacle version 9.2. After adjusting the MLC parameters to correlate with the film QA, there was still very good agreement between the Pinnacle model and commissioning data. Using the same QA methodology, we were also able to improve the beam models for the Varian C-series linacs, Novalis-Tx, and TrueBeam M-120 linacs.},
doi = {10.1118/1.4888458},
url = {https://www.osti.gov/biblio/22339882}, 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}
}