Optimization of solid tank design for fan-beam optical CT based 3D radiation dosimetry

Abstract

Optical computed tomography (CT) is one of the leading modalities for imaging gel dosimeters for 3D radiation dosimetry. There exist multiple scanner designs that have showcased excellent 3D dose verification capabilities of optical CT gel dosimetry. However, due to multiple experimental and reconstruction based factors there is currently no single scanner that has become a preferred standard. A significant challenge with setup and maintenance can be attributed to maintaining a large refractive index bath (1–15 l). In this work, a prototype solid ‘tank’ optical CT scanner is proposed that minimizes the volume of refractive index bath to between 10 and 35 ml. A ray-path simulator was created to optimize the design such that the solid tank geometry maximizes light collection across the detector array, maximizes the volume of the dosimeter scanned, and maximizes the collected signal dynamic range. An objective function was created to score possible geometries, and was optimized to find a local maximum geometry score from a set of possible design parameters. The design parameters optimized include the block length x bl , bore position x bc , fan-laser position x lp , lens block face semi-major axis length x ma , and the lens block face eccentricity x be . For the proposed design it was found that each of these parameters can have a significant effect on the signal collection efficacy within the scanner. Simulations scores are specific to the attenuation characteristics and refractive index of a simulated dosimeter. It was found that for a FlexyDos3D dosimeter, the ideal values for each of the five variables were: x bl = 314 mm, x bc = 6.5 mm, x lp = 50 mm, x ma = 66 mm, and x be = 0. In addition, a ClearView™ dosimeter was found to have ideal values at: x bl = 204 mm, x bc = 13 mm, x lp = 58 mm, x ma = 69 mm, and x be = 0. The ray simulator can also be used for further design and testing of new, unique and purpose-built optical CT geometries.

Superiorization versus regularization: A comparison of algorithms for solving image reconstruction problems with applications in computed tomography

“…We acknowledge that the system matrices used for this experiment are standard parallel‐beam and fan‐beam systems and do not incorporate the refraction properties present in optical CT. The current optical CT system being used by our research group is still in development 32 and hence no accurate system matrices were available. Nonetheless, this work presents a valuable step in working towards the goal of designing an effective optical CT system for radiotherapy dose verification.…”

Iterative Image Reconstruction Methodology in Optical CT Radiochromic Gel Dosimetry

“…An in-house ray tracing simulator has been developed to track the path of each ray as it traverses the different mediums of the prototype tabletop solid-tank fan-beam optical CT scanner developed at the University of British Columbia -Okanagan (Figure1) [8]. The scanner consists of an acrylic (PMMA) block with a curved face and a hole bored through it in which a cylindrical radiochromic gel dosimeter is inserted.…”

“…Figure1. Ray tracing simulator produced visual representation of primary (green) and crossover (red) raypaths through the prototype optical CT system of[8].…”

Preliminary commissioning of a prototype solid tank optical CT scanner for 3D radiation dosimetry

“…The rationale behind the design, as well as the procedure have been discussed in-depth in a previously published paper [12]. The prototype fan-beam scanner features a 635nm laser diode with a 60° linegenerating Powell lens.…”

“…Previously published work has demonstrated that a solid tank scanner with a severely reduced need for index matching can be built and optimized given a set of design criteria [12]. The purpose of this work is to commission the design found from that previous research.…”