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On the feasibility of optical-CT imaging in media of different refractive index.

Publication ,  Journal Article
Rankine, L; Oldham, M
Published in: Med Phys
May 2013

PURPOSE: Achieving accurate optical-CT 3D dosimetry without the use of viscous refractive index (RI) matching fluids would greatly increase convenience. METHODS: Software has been developed to simulate optical-CT 3D dosimetry for a range of scanning configurations including parallel-beam, point, and converging light sources. For each configuration the efficacy of three refractive media was investigated: air, water, a fluid closely matched to PRESAGE(®), and perfect matching (RI = 1.00, 1.33, 1.49, and 1.501 respectively). Reconstructions were performed using both filtered backprojection (FBP) and algebraic reconstruction technique (ART). The efficacy of the three configurations and the two algorithms was evaluated by calculating the usable radius (i.e., the outermost radius where data were accurate to within 2%), and gamma (Γ) analysis. This definition recognizes that for optical-CT imaging, errors are greatest near the edge of the dosimeter, where refraction can be most pronounced. Simulations were performed on three types of dose distribution: uniform, volumetric modulated arc therapy (VMAT), and brachytherapy (Cs-137). RESULTS: For a uniformly irradiated dosimeter the usable radius achieved with filtered backprojection was 68% for water-matching and 31% for dry-scanning in air. Algebraic reconstruction gave usable radii of 99% for both water and air (dry-scanning), indicating greater recovery of useful data for the uniform distribution. FBP and ART performed equally well for a VMAT dose distribution where less dose is delivered near the edge of the dosimeter. In this case, the usable radius was 86% and 53% for scanning in water and air, respectively. For brachytherapy, the usable radius was 99% and 98% for scanning in water and air, respectively using FBP, and a major decrease was seen with ART. Point source geometry provided 1%-2% larger usable radii than parallel geometry. Converging geometry recovered less usable dosimetry data (up to 10% reduced usable radii) than point and parallel geometries. A further disadvantage of converging geometry was an increased requirement on detector size by up to 18°. CONCLUSIONS: For applications where dose information is not required in the periphery of the dosimeter, some dry and low-viscous matching configurations may be feasible. For all three dose distributions (uniform, VMAT, brachytherapy) the point source geometry produced slightly more favorable results (an extra 1%-2% usable radii) than parallel and converging. When dosimetry is required on the periphery, best results were obtained using close refractive matching and ART. A concern for water or dry-scanning is the increase in required detector size, introducing potential cost penalties for manufacturing.

Duke Scholars

Published In

Med Phys

DOI

EISSN

2473-4209

Publication Date

May 2013

Volume

40

Issue

5

Start / End Page

051701

Location

United States

Related Subject Headings

  • Tomography, X-Ray Computed
  • Software
  • Radiotherapy, Intensity-Modulated
  • Radiometry
  • Optical Phenomena
  • Nuclear Medicine & Medical Imaging
  • Feasibility Studies
  • 5105 Medical and biological physics
  • 4003 Biomedical engineering
  • 1112 Oncology and Carcinogenesis
 

Citation

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MLA
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Rankine, L., & Oldham, M. (2013). On the feasibility of optical-CT imaging in media of different refractive index. Med Phys, 40(5), 051701. https://doi.org/10.1118/1.4798980
Rankine, Leith, and Mark Oldham. “On the feasibility of optical-CT imaging in media of different refractive index.Med Phys 40, no. 5 (May 2013): 051701. https://doi.org/10.1118/1.4798980.
Rankine L, Oldham M. On the feasibility of optical-CT imaging in media of different refractive index. Med Phys. 2013 May;40(5):051701.
Rankine, Leith, and Mark Oldham. “On the feasibility of optical-CT imaging in media of different refractive index.Med Phys, vol. 40, no. 5, May 2013, p. 051701. Pubmed, doi:10.1118/1.4798980.
Rankine L, Oldham M. On the feasibility of optical-CT imaging in media of different refractive index. Med Phys. 2013 May;40(5):051701.

Published In

Med Phys

DOI

EISSN

2473-4209

Publication Date

May 2013

Volume

40

Issue

5

Start / End Page

051701

Location

United States

Related Subject Headings

  • Tomography, X-Ray Computed
  • Software
  • Radiotherapy, Intensity-Modulated
  • Radiometry
  • Optical Phenomena
  • Nuclear Medicine & Medical Imaging
  • Feasibility Studies
  • 5105 Medical and biological physics
  • 4003 Biomedical engineering
  • 1112 Oncology and Carcinogenesis