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Title: Quantification of the impact of MLC modeling and tissue heterogeneities on dynamic IMRT dose calculations

Abstract

This study quantifies the dose prediction errors (DPEs) in dynamic IMRT dose calculations resulting from (a) use of an intensity matrix to estimate the multi-leaf collimator (MLC) modulated photon fluence (DPE{sub IGfluence}) instead of an explicit MLC particle transport, and (b) handling of tissue heterogeneities (DPE{sub hetero}) by superposition/convolution (SC) and pencil beam (PB) dose calculation algorithms. Monte Carlo (MC) computed doses are used as reference standards. Eighteen head-and-neck dynamic MLC IMRT treatment plans are investigated. DPEs are evaluated via comparing the dose received by 98% of the GTV (GTV D{sub 98%}), the CTV D{sub 95%}, the nodal D{sub 90%}, the cord and the brainstem D{sub 02%}, the parotid D{sub 50%}, the parotid mean dose (D{sub Mean}), and generalized equivalent uniform doses (gEUDs) for the above structures. For the MC-generated intensity grids, DPE{sub IGfluence} is within {+-}2.1% for all targets and critical structures. The SC algorithm DPE{sub hetero} is within {+-}3% for 98.3% of the indices tallied, and within {+-}3.4% for all of the tallied indices. The PB algorithm DPE{sub hetero} is within {+-}3% for 92% of the tallied indices. Statistical equivalence tests indicate that PB DPE{sub hetero} requires a {+-}3.6% interval to state equivalence with the MC standard, whilemore » the intervals are <1.5% for SC DPE{sub hetero} and DPE{sub IGfluence}. Overall, these results indicate that SC and MC IMRT dose calculations which use MC-derived intensity matrices for fluence prediction do not introduce significant dose errors compared with full Monte Carlo dose computations; however, PB algorithms may result in clinically significant dose deviations.« less

Authors:
; ; ;  [1];  [2]
  1. Department of Radiation Oncology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205 (United States) and Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia 23298 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20951145
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 34; Journal Issue: 4; Other Information: DOI: 10.1118/1.2712413; (c) 2007 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
61 RADIATION PROTECTION AND DOSIMETRY; ALGORITHMS; CALIBRATION STANDARDS; COLLIMATORS; ERRORS; FORECASTING; MONTE CARLO METHOD; NECK; RADIATION DOSES; RADIOTHERAPY; SIMULATION

Citation Formats

Mihaylov, I. B., Lerma, F. A., Fatyga, M., Siebers, J. V., and Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia 23298. Quantification of the impact of MLC modeling and tissue heterogeneities on dynamic IMRT dose calculations. United States: N. p., 2007. Web. doi:10.1118/1.2712413.
Mihaylov, I. B., Lerma, F. A., Fatyga, M., Siebers, J. V., & Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia 23298. Quantification of the impact of MLC modeling and tissue heterogeneities on dynamic IMRT dose calculations. United States. doi:10.1118/1.2712413.
Mihaylov, I. B., Lerma, F. A., Fatyga, M., Siebers, J. V., and Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia 23298. Sun . "Quantification of the impact of MLC modeling and tissue heterogeneities on dynamic IMRT dose calculations". United States. doi:10.1118/1.2712413.
@article{osti_20951145,
title = {Quantification of the impact of MLC modeling and tissue heterogeneities on dynamic IMRT dose calculations},
author = {Mihaylov, I. B. and Lerma, F. A. and Fatyga, M. and Siebers, J. V. and Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia 23298},
abstractNote = {This study quantifies the dose prediction errors (DPEs) in dynamic IMRT dose calculations resulting from (a) use of an intensity matrix to estimate the multi-leaf collimator (MLC) modulated photon fluence (DPE{sub IGfluence}) instead of an explicit MLC particle transport, and (b) handling of tissue heterogeneities (DPE{sub hetero}) by superposition/convolution (SC) and pencil beam (PB) dose calculation algorithms. Monte Carlo (MC) computed doses are used as reference standards. Eighteen head-and-neck dynamic MLC IMRT treatment plans are investigated. DPEs are evaluated via comparing the dose received by 98% of the GTV (GTV D{sub 98%}), the CTV D{sub 95%}, the nodal D{sub 90%}, the cord and the brainstem D{sub 02%}, the parotid D{sub 50%}, the parotid mean dose (D{sub Mean}), and generalized equivalent uniform doses (gEUDs) for the above structures. For the MC-generated intensity grids, DPE{sub IGfluence} is within {+-}2.1% for all targets and critical structures. The SC algorithm DPE{sub hetero} is within {+-}3% for 98.3% of the indices tallied, and within {+-}3.4% for all of the tallied indices. The PB algorithm DPE{sub hetero} is within {+-}3% for 92% of the tallied indices. Statistical equivalence tests indicate that PB DPE{sub hetero} requires a {+-}3.6% interval to state equivalence with the MC standard, while the intervals are <1.5% for SC DPE{sub hetero} and DPE{sub IGfluence}. Overall, these results indicate that SC and MC IMRT dose calculations which use MC-derived intensity matrices for fluence prediction do not introduce significant dose errors compared with full Monte Carlo dose computations; however, PB algorithms may result in clinically significant dose deviations.},
doi = {10.1118/1.2712413},
journal = {Medical Physics},
number = 4,
volume = 34,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}