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A method to correct for stray light in telecentric optical-CT imaging of radiochromic dosimeters.

Publication ,  Journal Article
Thomas, A; Newton, J; Oldham, M
Published in: Phys Med Biol
July 21, 2011

Radiochromic plastic and gel materials have recently emerged which can yield 3D dose information over clinical volumes in high resolution. These dosimeters can provide a much more comprehensive verification of complex radiation therapy treatments than can be achieved by conventional planar and point dosimeters. To achieve full clinical potential, these dosimeters require a fast and accurate read-out technology. Broad-beam optical-computed tomography (optical-CT) systems have shown promise, but can be sensitive to stray light artifacts originating in the imaging chain. In this work we present and evaluate a method to correct for stray light artifacts by deconvolving a measured, spatially invariant, point spread function (PSF). The correction was developed for the DLOS (Duke large field-of-view optical-CT scanner) in conjunction with radiochromic PRESAGE® dosimeters. The PSF was constructed from a series of acquisitions of projection images of various sized apertures placed in the optical imaging chain. Images were acquired with a range of exposure times, and for a range of aperture sizes (0.2-11 mm). The PSF is investigated under a variety of conditions, and found to be robust and spatially invariant, key factors enabling the viability of the deconvolution approach. The spatial invariance and robustness of the PSF are facilitated by telecentric imaging, which produces a collimated light beam and removes stray light originating upstream of the imaging lens. The telecentric capability of the DLOS therefore represents a significant advantage, both in keeping stray light levels to a minimum and enabling viability of an accurate PSF deconvolution method to correct for the residual. The performance of the correction method was evaluated on projection images containing known optical-density variations, and also on known 3D dose distributions. The method is shown to accurately account for stray light on small field dosimetry with corrections up to 3% in magnitude shown here although corrections of >10% have been observed in extreme cases. The dominant source of stray light was found to be within the imaging lens. Correcting for stray light extended the dynamic range of the system from ∼30 to ∼60 dB. The correction should be used when measurements need to be accurate within 3%.

Duke Scholars

Published In

Phys Med Biol

DOI

EISSN

1361-6560

Publication Date

July 21, 2011

Volume

56

Issue

14

Start / End Page

4433 / 4451

Location

England

Related Subject Headings

  • Tomography, X-Ray Computed
  • Scattering, Radiation
  • Radiometry
  • Optical Phenomena
  • Nuclear Medicine & Medical Imaging
  • Light
  • Artifacts
  • 5105 Medical and biological physics
  • 1103 Clinical Sciences
  • 0903 Biomedical Engineering
 

Citation

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Thomas, A., Newton, J., & Oldham, M. (2011). A method to correct for stray light in telecentric optical-CT imaging of radiochromic dosimeters. Phys Med Biol, 56(14), 4433–4451. https://doi.org/10.1088/0031-9155/56/14/013
Thomas, Andrew, Joseph Newton, and Mark Oldham. “A method to correct for stray light in telecentric optical-CT imaging of radiochromic dosimeters.Phys Med Biol 56, no. 14 (July 21, 2011): 4433–51. https://doi.org/10.1088/0031-9155/56/14/013.
Thomas A, Newton J, Oldham M. A method to correct for stray light in telecentric optical-CT imaging of radiochromic dosimeters. Phys Med Biol. 2011 Jul 21;56(14):4433–51.
Thomas, Andrew, et al. “A method to correct for stray light in telecentric optical-CT imaging of radiochromic dosimeters.Phys Med Biol, vol. 56, no. 14, July 2011, pp. 4433–51. Pubmed, doi:10.1088/0031-9155/56/14/013.
Thomas A, Newton J, Oldham M. A method to correct for stray light in telecentric optical-CT imaging of radiochromic dosimeters. Phys Med Biol. 2011 Jul 21;56(14):4433–4451.
Journal cover image

Published In

Phys Med Biol

DOI

EISSN

1361-6560

Publication Date

July 21, 2011

Volume

56

Issue

14

Start / End Page

4433 / 4451

Location

England

Related Subject Headings

  • Tomography, X-Ray Computed
  • Scattering, Radiation
  • Radiometry
  • Optical Phenomena
  • Nuclear Medicine & Medical Imaging
  • Light
  • Artifacts
  • 5105 Medical and biological physics
  • 1103 Clinical Sciences
  • 0903 Biomedical Engineering