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Title: SU-F-T-142: An Analytical Model to Correct the Aperture Scattered Dose in Clinical Proton Beams

Abstract

Purpose: Apertures or collimators are used to laterally shape proton beams in double scattering (DS) delivery and to sharpen the penumbra in pencil beam (PB) delivery. However, aperture-scattered dose is not included in the current dose calculations of treatment planning system (TPS). The purpose of this study is to provide a method to correct the aperture-scattered dose based on an analytical model. Methods: A DS beam with a non-divergent aperture was delivered using a single-room proton machine. Dose profiles were measured with an ion-chamber scanning in water and a 2-D ion chamber matrix with solid-water buildup at various depths. The measured doses were considered as the sum of the non-contaminated dose and the aperture-scattered dose. The non-contaminated dose was calculated by TPS and subtracted from the measured dose. Aperture scattered-dose was modeled as a 1D Gaussian distribution. For 2-D fields, to calculate the scatter-dose from all the edges of aperture, a sum of weighted distance was used in the model based on the distance from calculation point to aperture edge. The gamma index was calculated between the measured and calculated dose with and without scatter correction. Results: For a beam with range of 23 cm and aperture size of 20more » cm, the contribution of the scatter horn was ∼8% of the total dose at 4 cm depth and diminished to 0 at 15 cm depth. The amplitude of scatter-dose decreased linearly with the depth increase. The 1D gamma index (2%/2 mm) between the calculated and measured profiles increased from 63% to 98% for 4 cm depth and from 83% to 98% at 13 cm depth. The 2D gamma index (2%/2 mm) at 4 cm depth has improved from 78% to 94%. Conclusion: Using the simple analytical method the discrepancy between the measured and calculated dose has significantly improved.« less

Authors:
;  [1]; ;  [2];  [3]; ;  [4]; ;  [5]
  1. Washington University in St. Louis, St. Louis, MO (United States)
  2. Washington University School of Medicine, St. Louis, MO (United States)
  3. Washington University in St Louis, St Louis, MO (United States)
  4. Washington University, St. Louis, MO (United States)
  5. Washington University School of Medicine, Saint Louis, MO (United States)
Publication Date:
OSTI Identifier:
22642383
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:
60 APPLIED LIFE SCIENCES; APERTURES; CORRECTIONS; GAUSS FUNCTION; IONIZATION CHAMBERS; PROTON BEAMS; RADIATION DOSES; RADIOTHERAPY; SCATTERING

Citation Formats

Sun, B, Liu, S, Zhang, T, Zhao, T, Yang, D, Grantham, K, Goddu, S, Bradley, J, and Mutic, S. SU-F-T-142: An Analytical Model to Correct the Aperture Scattered Dose in Clinical Proton Beams. United States: N. p., 2016. Web. doi:10.1118/1.4956278.
Sun, B, Liu, S, Zhang, T, Zhao, T, Yang, D, Grantham, K, Goddu, S, Bradley, J, & Mutic, S. SU-F-T-142: An Analytical Model to Correct the Aperture Scattered Dose in Clinical Proton Beams. United States. doi:10.1118/1.4956278.
Sun, B, Liu, S, Zhang, T, Zhao, T, Yang, D, Grantham, K, Goddu, S, Bradley, J, and Mutic, S. Wed . "SU-F-T-142: An Analytical Model to Correct the Aperture Scattered Dose in Clinical Proton Beams". United States. doi:10.1118/1.4956278.
@article{osti_22642383,
title = {SU-F-T-142: An Analytical Model to Correct the Aperture Scattered Dose in Clinical Proton Beams},
author = {Sun, B and Liu, S and Zhang, T and Zhao, T and Yang, D and Grantham, K and Goddu, S and Bradley, J and Mutic, S},
abstractNote = {Purpose: Apertures or collimators are used to laterally shape proton beams in double scattering (DS) delivery and to sharpen the penumbra in pencil beam (PB) delivery. However, aperture-scattered dose is not included in the current dose calculations of treatment planning system (TPS). The purpose of this study is to provide a method to correct the aperture-scattered dose based on an analytical model. Methods: A DS beam with a non-divergent aperture was delivered using a single-room proton machine. Dose profiles were measured with an ion-chamber scanning in water and a 2-D ion chamber matrix with solid-water buildup at various depths. The measured doses were considered as the sum of the non-contaminated dose and the aperture-scattered dose. The non-contaminated dose was calculated by TPS and subtracted from the measured dose. Aperture scattered-dose was modeled as a 1D Gaussian distribution. For 2-D fields, to calculate the scatter-dose from all the edges of aperture, a sum of weighted distance was used in the model based on the distance from calculation point to aperture edge. The gamma index was calculated between the measured and calculated dose with and without scatter correction. Results: For a beam with range of 23 cm and aperture size of 20 cm, the contribution of the scatter horn was ∼8% of the total dose at 4 cm depth and diminished to 0 at 15 cm depth. The amplitude of scatter-dose decreased linearly with the depth increase. The 1D gamma index (2%/2 mm) between the calculated and measured profiles increased from 63% to 98% for 4 cm depth and from 83% to 98% at 13 cm depth. The 2D gamma index (2%/2 mm) at 4 cm depth has improved from 78% to 94%. Conclusion: Using the simple analytical method the discrepancy between the measured and calculated dose has significantly improved.},
doi = {10.1118/1.4956278},
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}
}