Technical Note: Validation of halo modeling for proton pencil beam spot scanning using a quality assurance test pattern

Liyong Lin, Sheng Huang, Minglei Kang, Timothy D. Solberg, James E. McDonough, Christopher G. Ainsley

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Purpose: The purpose of this paper is to demonstrate the utility of a comprehensive test pattern in validating calculation models that include the halo component (low-dose tails) of proton pencil beam scanning (PBS) spots. Such a pattern has been used previously for quality assurance purposes to assess spot shape, position, and dose. Methods: In this study, a scintillation detector was used to measure the test pattern in air at isocenter for two proton beam energies (115 and 225 MeV) of two IBA universal nozzles (UN #1 and UN #2). Planar measurements were compared with calculated dose distributions based on the weighted superposition of location-independent (UN #1) or location-dependent (UN #2) spot profiles, previously measured using a pair-magnification method and between two nozzles. Results: Including the halo component below 1% of the central dose is shown to improve the gamma-map comparison between calculation and measurement from 94.9% to 98.4% using 2mm/2% criteria for the 115 MeV proton beam of UN #1. In contrast, including the halo component below 1% of the central dose does not improve the gamma agreement for the 115 MeV proton beam of UN #2, due to the cutoff of the halo component at off-axis locations. When location-dependent spot profiles are used for calculation instead of spot profiles at central axis, the gamma agreement is improved from 98.0% to 99.5% using 2 mm/2% criteria. The two nozzles clearly have different characteristics, as a direct comparison of measured data shows a passing rate of 89.7% for the 115 MeV proton beam. At 225 MeV, the corresponding gamma comparisons agree better between measurement and calculation, and between measurements in the two nozzles. Conclusions: In addition to confirming the primary component of individual PBS spot profiles, a comprehensive test pattern is useful for the validation of the halo component at off-axis locations, especially for low energy protons.

Original languageEnglish (US)
Pages (from-to)5138-5143
Number of pages6
JournalMedical Physics
Volume42
Issue number9
DOIs
StatePublished - Sep 1 2015

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Protons
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Keywords

  • commissioning
  • halo
  • pencil beam scanning
  • proton therapy
  • quality assurance

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging

Cite this

Technical Note : Validation of halo modeling for proton pencil beam spot scanning using a quality assurance test pattern. / Lin, Liyong; Huang, Sheng; Kang, Minglei; Solberg, Timothy D.; McDonough, James E.; Ainsley, Christopher G.

In: Medical Physics, Vol. 42, No. 9, 01.09.2015, p. 5138-5143.

Research output: Contribution to journalArticle

Lin, Liyong ; Huang, Sheng ; Kang, Minglei ; Solberg, Timothy D. ; McDonough, James E. ; Ainsley, Christopher G. / Technical Note : Validation of halo modeling for proton pencil beam spot scanning using a quality assurance test pattern. In: Medical Physics. 2015 ; Vol. 42, No. 9. pp. 5138-5143.
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abstract = "Purpose: The purpose of this paper is to demonstrate the utility of a comprehensive test pattern in validating calculation models that include the halo component (low-dose tails) of proton pencil beam scanning (PBS) spots. Such a pattern has been used previously for quality assurance purposes to assess spot shape, position, and dose. Methods: In this study, a scintillation detector was used to measure the test pattern in air at isocenter for two proton beam energies (115 and 225 MeV) of two IBA universal nozzles (UN #1 and UN #2). Planar measurements were compared with calculated dose distributions based on the weighted superposition of location-independent (UN #1) or location-dependent (UN #2) spot profiles, previously measured using a pair-magnification method and between two nozzles. Results: Including the halo component below 1{\%} of the central dose is shown to improve the gamma-map comparison between calculation and measurement from 94.9{\%} to 98.4{\%} using 2mm/2{\%} criteria for the 115 MeV proton beam of UN #1. In contrast, including the halo component below 1{\%} of the central dose does not improve the gamma agreement for the 115 MeV proton beam of UN #2, due to the cutoff of the halo component at off-axis locations. When location-dependent spot profiles are used for calculation instead of spot profiles at central axis, the gamma agreement is improved from 98.0{\%} to 99.5{\%} using 2 mm/2{\%} criteria. The two nozzles clearly have different characteristics, as a direct comparison of measured data shows a passing rate of 89.7{\%} for the 115 MeV proton beam. At 225 MeV, the corresponding gamma comparisons agree better between measurement and calculation, and between measurements in the two nozzles. Conclusions: In addition to confirming the primary component of individual PBS spot profiles, a comprehensive test pattern is useful for the validation of the halo component at off-axis locations, especially for low energy protons.",
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