Abstract
Telecentric optical computed tomography (optical-CT) is a state-of-the-art method for visualizing and quantifying 3-dimensional dose distributions in radiochromic dosimeters. In this work a prototype telecentric system (DFOS—Duke Fresnel Optical-CT Scanner) is evaluated which incorporates two substantial design changes: the use of Fresnel lenses (reducing lens costs from $10-30K t0 $1-3K) and the use of a ‘solid tank’ (which reduces noise, and the volume of refractively matched fluid from 1ltr to 10cc). The efficacy of DFOS was evaluated by direct comparison against commissioned scanners in our lab. Measured dose distributions from all systems were compared against the predicted dose distributions from a commissioned treatment planning system (TPS). Three treatment plans were investigated including a simple four-field box treatment, a multiple small field delivery, and a complex IMRT treatment. Dosimeters were imaged within 2h post irradiation, using consistent scanning techniques (360 projections acquired at 1 degree intervals, reconstruction at 2mm). DFOS efficacy was evaluated through inspection of dose line-profiles, and 2D and 3D dose and gamma maps. DFOS/TPS gamma pass rates with 3%/3mm dose difference/distance-to-agreement criteria ranged from 89.3% to 92.2%, compared to from 95.6% to 99.0% obtained with the commissioned system. The 3D gamma pass rate between the commissioned system and DFOS was 98.2%. The typical noise rates in DFOS reconstructions were up to 3%, compared to under 2% for the commissioned system. In conclusion, while the introduction of a solid tank proved advantageous with regards to cost and convenience, further work is required to improve the image quality and dose reconstruction accuracy of the new DFOS optical-CT system.
Highlights
Optical computed tomography is a technique for imaging 3D dose distributions in radiochromic and gel dosimeters [1,2] It is the visible light analog of X-ray CT in that linearPLOS ONE | DOI:10.1371/journal.pone.0152606 March 28, 2016Optical-CT with Fresnel Lenses and Minimal Matching Fluid attenuation coefficients of visible light are reconstructed throughout a partially transparent dosimeter
We explore the feasibility of accurate 3D dosimetry with the DFOS scanner incorporating two innovations: the solid tank which reduces the amount of refractive index (RI) matching fluid by 98%; and the utilization of Fresnel lenses
Utilization of a solid-tank has benefits in reducing fluid and fluid management overheads, but our data show that ring artifacts and overall noise are increased with the use if a solid tank and Fresnel lenses
Summary
Optical computed tomography (optical-CT) is a technique for imaging 3D dose distributions in radiochromic and gel dosimeters [1,2] It is the visible light analog of X-ray CT in that linearPLOS ONE | DOI:10.1371/journal.pone.0152606 March 28, 2016Optical-CT with Fresnel Lenses and Minimal Matching Fluid attenuation coefficients of visible light are reconstructed throughout a partially transparent dosimeter. Optical-CT has been used as an alternative to MRI-readout of Fricke dosimeters, which exhibit a dose-dependent oxidation of Fe2+ ions, resulting in an optical density change [6,7,8,9] Radiochromic plastic dosimeters such as Presage (PRESAGE1) (Hueris, Skillman, NJ) have been well documented [10,11,12,13,14] and have been shown to exhibit a linear dose response, water/ tissue equivalency, insensitivity to ambient light and temperature, and require no external case or mold, allowing a variety of physical alterations. The highly transparent polyurethane matrix of Presage, coupled with the light absorbing nature of the radiochromic dye (Malachite Green analog), renders Presage amenable to accurate optical-CT dosimetry by virtue of the very low-level of contaminant stray light
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