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Title: SU-D-BRC-06: Experimental and Monte Carlo Studies of Fluence Corrections for Graphite Calorimetry in Proton Therapy

Abstract

Purpose: For photon and electron beams, the standard device used to measure absorbed dose is a calorimeter. Standards laboratories are currently working on the establishment of graphite calorimeters as a primary standard for proton beams. To provide a practical method for graphite calorimetry, it is necessary to convert dose to graphite to dose to water, requiring knowledge of the water-to-graphite stopping-power ratio and the fluence correction factor. This study aims to present a novel method to determine fluence corrections experimentally, and to apply this methodology to low- and high-energy proton beams. Methods: Measurements were performed in 60 MeV and 180 MeV proton beams. Experimental information was obtained from depth-dose ionization chamber measurements performed in a water phantom. This was repeated with different thicknesses of graphite plates in front of the water phantom. One distinct advantage of this method is that only ionization chamber perturbation factors for water are required. Fluence corrections were also obtained through Monte Carlo simulations for comparison with the experiments. Results: The experimental observations made in this study confirm the Monte Carlo results. Overall, fluence corrections between water and graphite increased with depth, with a maximum correction of 1% for the low-energy beam and 4% for themore » high-energy beam. The results also showed that a fraction of the secondary particles generated in proton therapy beams do not have enough energy to cross the ionization chamber wall; thus, their contribution is not accounted for in the measured fluence corrections. This effect shows up as a discrepancy in fluence corrections of 1% and has been confirmed by simulations of the experimental setup. Conclusion: Fluence corrections derived by experiment do not account for low-energy secondary particles that are stopped in the ion chamber wall. This work will contribute to a practical graphite calorimetry technique for determining absolute dose to water in proton beams.« less

Authors:
 [1];  [2];  [3];  [4];  [5];  [6];  [1];  [3];  [7]
  1. University College London, London (United Kingdom)
  2. (United Kingdom)
  3. National Physical Laboratory, Teddington (United Kingdom)
  4. University of Montreal, Montreal (Canada)
  5. National Eye Proton therapy Centre, Clatterbridge Cancer Centre, Wirral (United Kingdom)
  6. Proton Therapy Center, Prague (Czech Republic)
  7. (Austria)
Publication Date:
OSTI Identifier:
22624377
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
07 ISOTOPES AND RADIATION SOURCES; 60 APPLIED LIFE SCIENCES; ABSORBED RADIATION DOSES; CALORIMETERS; CALORIMETRY; COMPUTERIZED SIMULATION; CORRECTIONS; DEPTH DOSE DISTRIBUTIONS; ELECTRON BEAMS; GRAPHITE; IONIZATION CHAMBERS; MONTE CARLO METHOD; PHANTOMS; PROTON BEAMS; RADIOTHERAPY

Citation Formats

Lourenco, A, National Physical Laboratory, Teddington, Thomas, R, Bouchard, H, Kacperek, A, Vondracek, V, Royle, G, Palmans, H, and EBG MedAustron GmbH, Wiener Neustadt. SU-D-BRC-06: Experimental and Monte Carlo Studies of Fluence Corrections for Graphite Calorimetry in Proton Therapy. United States: N. p., 2016. Web. doi:10.1118/1.4955625.
Lourenco, A, National Physical Laboratory, Teddington, Thomas, R, Bouchard, H, Kacperek, A, Vondracek, V, Royle, G, Palmans, H, & EBG MedAustron GmbH, Wiener Neustadt. SU-D-BRC-06: Experimental and Monte Carlo Studies of Fluence Corrections for Graphite Calorimetry in Proton Therapy. United States. doi:10.1118/1.4955625.
Lourenco, A, National Physical Laboratory, Teddington, Thomas, R, Bouchard, H, Kacperek, A, Vondracek, V, Royle, G, Palmans, H, and EBG MedAustron GmbH, Wiener Neustadt. Wed . "SU-D-BRC-06: Experimental and Monte Carlo Studies of Fluence Corrections for Graphite Calorimetry in Proton Therapy". United States. doi:10.1118/1.4955625.
@article{osti_22624377,
title = {SU-D-BRC-06: Experimental and Monte Carlo Studies of Fluence Corrections for Graphite Calorimetry in Proton Therapy},
author = {Lourenco, A and National Physical Laboratory, Teddington and Thomas, R and Bouchard, H and Kacperek, A and Vondracek, V and Royle, G and Palmans, H and EBG MedAustron GmbH, Wiener Neustadt},
abstractNote = {Purpose: For photon and electron beams, the standard device used to measure absorbed dose is a calorimeter. Standards laboratories are currently working on the establishment of graphite calorimeters as a primary standard for proton beams. To provide a practical method for graphite calorimetry, it is necessary to convert dose to graphite to dose to water, requiring knowledge of the water-to-graphite stopping-power ratio and the fluence correction factor. This study aims to present a novel method to determine fluence corrections experimentally, and to apply this methodology to low- and high-energy proton beams. Methods: Measurements were performed in 60 MeV and 180 MeV proton beams. Experimental information was obtained from depth-dose ionization chamber measurements performed in a water phantom. This was repeated with different thicknesses of graphite plates in front of the water phantom. One distinct advantage of this method is that only ionization chamber perturbation factors for water are required. Fluence corrections were also obtained through Monte Carlo simulations for comparison with the experiments. Results: The experimental observations made in this study confirm the Monte Carlo results. Overall, fluence corrections between water and graphite increased with depth, with a maximum correction of 1% for the low-energy beam and 4% for the high-energy beam. The results also showed that a fraction of the secondary particles generated in proton therapy beams do not have enough energy to cross the ionization chamber wall; thus, their contribution is not accounted for in the measured fluence corrections. This effect shows up as a discrepancy in fluence corrections of 1% and has been confirmed by simulations of the experimental setup. Conclusion: Fluence corrections derived by experiment do not account for low-energy secondary particles that are stopped in the ion chamber wall. This work will contribute to a practical graphite calorimetry technique for determining absolute dose to water in proton beams.},
doi = {10.1118/1.4955625},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = {Wed Jun 15 00:00:00 EDT 2016},
month = {Wed Jun 15 00:00:00 EDT 2016}
}