Open Collections

Ogilvy, Andy

University of British Columbia

Three-dimensional dosimeters have potential to advance radiation treatment through comprehensive three-dimensional dose verification. While they offer a distinct advantage, their application is intricate, requiring specialized expertise for accurate readout. Optical computed tomography (CT) stands out as a primary modality for imaging three-dimensional dosimeters used in validating complex radiotherapy treatments. The objectives of this thesis are to (1) develop a ray-tracing simulator capable of calculating an optimized optical CT geometry given the optical properties of the dosimeter and manufacturing materials, (2) design, optimize, manufacture, and commission a fan-beam solid tank optical CT scanner for use on FlexyDos3D dosimeters, and (3) update the ray-tracing simulator to enable optimization for small-detection system scanners. A ray-tracing simulator was developed to find an optimized geometry for a prototype solid tank optical CT scanner. Five geometric variables were adjusted to assess the geometry’s performance based on three properties: effective radius, magnification, and beam uniformity. The optimization workflow flexibility was demonstrated by finding optimal geometries for two optically different 3D dosimeters, FlexyDos3D and ClearView™. An optimized optical CT scanner design for FlexyDos3D dosimeters was manufactured and commissioned. The prototype scanner exhibited a maximum spatial resolution of MTF₅₀ of 0.929 mm⁻¹. Geometric distortion was evaluated, revealing a center-of-intensity needle alignment of <0.25 mm irrespective of needle location. The system’s contrast-to-noise peak varied from 65-190, depending on the sample region for background attenuation. Iterative reconstruction was performed using the FISTA algorithm with a total reconstruction time of around 3 minutes for 200 iterations. The ray-tracing simulator was adapted to facilitate the optimization of designs utilizing small-detection systems such as CCD or CMOS detectors by shaping the acrylic block rear wall as a focusing lens. A high-scoring geometry is created by perturbing the rear lens using the proposed discretized lens creation method. The resulting lens converges all rays to a singular focal point, avoiding the aberrations found in conic lenses.

Text

2024-01-12

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/87225

Medical Physics

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/