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Title: Reconstruction of electron spectra from depth doses with adaptive regularization

Abstract

Electron spectral reconstruction of medical accelerators from measured depth doses is a practical method for providing the input initial phase space distribution at the patient surface that is required by Monte Carlo treatment planning systems. The posed inverse problem of spectral reconstruction is ill conditioned and this may lead to nonphysical oscillations in the reconstructed spectra. Use of a variational method of solution with a regularization technique removes the oscillations but tends to smooth the sharp (deltalike) energy peak that is a common feature in electron spectra generated by medical accelerators. Because the sharp peak contains a large percentage of the electrons in the spectrum, an accurate estimate of the peak width, height and position is critical to the success of the technique for spectrum reconstruction with regularization. We propose use of an adaptive regularization term as a special form of the general Tichonov regularization function. The variational method with the adaptive regularization term is applied to reconstruct electron spectra for the 6, 9, and 18 MeV electron beams of a Varian Clinac 2100C accelerator and proves to be a very simple, effective and accurate approach. Results using this variational method with adaptive regularization almost perfectly reconstruct electron spectra frommore » depth dose distributions.« less

Authors:
; ;  [1];  [2]
  1. School of Health Sciences, Purdue University, West Lafayette, Indiana 47907 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20775059
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 33; Journal Issue: 2; Other Information: DOI: 10.1118/1.2161404; (c) 2006 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; ACCELERATORS; DEPTH DOSE DISTRIBUTIONS; DOSIMETRY; ELECTRON BEAMS; ELECTRON SPECTRA; MONTE CARLO METHOD; PATIENTS; PHASE SPACE; PLANNING; RADIOTHERAPY; VARIATIONAL METHODS

Citation Formats

Wei Jikun, Sandison, George A., Chvetsov, Alexei V., and Department of Radiation Oncology, Case Western Reserve University and University Hospitals of Cleveland, Cleveland, Ohio 44106-6068. Reconstruction of electron spectra from depth doses with adaptive regularization. United States: N. p., 2006. Web. doi:10.1118/1.2161404.
Wei Jikun, Sandison, George A., Chvetsov, Alexei V., & Department of Radiation Oncology, Case Western Reserve University and University Hospitals of Cleveland, Cleveland, Ohio 44106-6068. Reconstruction of electron spectra from depth doses with adaptive regularization. United States. doi:10.1118/1.2161404.
Wei Jikun, Sandison, George A., Chvetsov, Alexei V., and Department of Radiation Oncology, Case Western Reserve University and University Hospitals of Cleveland, Cleveland, Ohio 44106-6068. Wed . "Reconstruction of electron spectra from depth doses with adaptive regularization". United States. doi:10.1118/1.2161404.
@article{osti_20775059,
title = {Reconstruction of electron spectra from depth doses with adaptive regularization},
author = {Wei Jikun and Sandison, George A. and Chvetsov, Alexei V. and Department of Radiation Oncology, Case Western Reserve University and University Hospitals of Cleveland, Cleveland, Ohio 44106-6068},
abstractNote = {Electron spectral reconstruction of medical accelerators from measured depth doses is a practical method for providing the input initial phase space distribution at the patient surface that is required by Monte Carlo treatment planning systems. The posed inverse problem of spectral reconstruction is ill conditioned and this may lead to nonphysical oscillations in the reconstructed spectra. Use of a variational method of solution with a regularization technique removes the oscillations but tends to smooth the sharp (deltalike) energy peak that is a common feature in electron spectra generated by medical accelerators. Because the sharp peak contains a large percentage of the electrons in the spectrum, an accurate estimate of the peak width, height and position is critical to the success of the technique for spectrum reconstruction with regularization. We propose use of an adaptive regularization term as a special form of the general Tichonov regularization function. The variational method with the adaptive regularization term is applied to reconstruct electron spectra for the 6, 9, and 18 MeV electron beams of a Varian Clinac 2100C accelerator and proves to be a very simple, effective and accurate approach. Results using this variational method with adaptive regularization almost perfectly reconstruct electron spectra from depth dose distributions.},
doi = {10.1118/1.2161404},
journal = {Medical Physics},
number = 2,
volume = 33,
place = {United States},
year = {Wed Feb 15 00:00:00 EST 2006},
month = {Wed Feb 15 00:00:00 EST 2006}
}