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Title: Development of the DEPICT system for gamma-ray imaging in molecular radiotherapy
Author: McAreavey, Lucy H.
ISNI:       0000 0004 7970 5088
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2019
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The development and evaluation of a gamma-ray imaging system for dosimetry of Molecular Radiotherapy (MRT) is presented. MRT is a cancer treatment that aims to deliver high radiation doses to targeted tumour or disease sites, with minimal dose to surrounding healthy tissue. This is achieved through the administration of radiopharmaceuticals, typically with a fixed activity or adjusted for patient weight or body surface area. These activities are often several gigabecquerels (GBq). The administered radionuclide decays via the emission of charged particles which damage the cancerous or diseased cells, ideally alongside gamma rays that can be used to image the distribution of the radiopharmaceutical. The absorbed dose in regions of interest can then be calculated by extracting activity from these images. However, the energy resolution, spatial resolution and count rate performance of current clinical gamma-ray imaging systems result in inaccurate activity calculations. The Dosimetric Imaging with Cadmium Zinc Telluride (DEPICT) project aims to overcome these performance limitations through the development of an optimised gamma camera system, configured with a 3D printed tungsten collimator and Cadmium Zinc Telluride (CZT) detectors. This thesis focuses on the optimisation of the DEPICT system for 131I, which is used for MRT treatment of the thyroid. This will provide improved verification of these treatments and information that allows subsequent personalisation of the otherwise generic treatment plans. A pixelated CZT detector was selected because of its excellent energy resolution and spatial resolution. The DEPICT CZT detector was characterised and an experimental study undertaken to optimise the energy resolution and throughput of gamma rays. The optimum energy resolution at 364.5 keV was shown to be 2.94% for a maximum count rate of 160 kcps. A 3D printed highenergy parallel-hole tungsten collimator suitable for imaging the 364.5 keV gamma rays from 131I was developed. Experimental data were acquired with medical phantoms to determine the imaging capability DEPICT, as accurate area delineation is necessary for measurements of activity within a region of interest. The spatial resolution of DEPICT was shown to be 2 mm, which is superior to 13.4 mm for clinical systems that are configured with high-energy collimators. Methodology for quantifying the sizes of artefacts in an image are described. The experimental performance of DEPICT for imaging 131I distributed in a thyroid phantom was shown to surpass that of a clinical Siemens gamma camera. It was possible to identify regions of interest in the DEPICT thyroid phantom image that were not visible in the clinical image, due to the improved spatial and energy resolution. Quantification of the activity in vials containing 131I has been achieved using DEPICT to within 9% of the known activity for data acquired with 1 vial and 3% for data with 3 vials. Distributed sources have also been visualised in 3D using tomography, to show the capability of accurately reconstructing volumes of interest. The future of MRT relies on the development of innovative radiopharmaceuticals. The radionuclides 177Lu, 111In, 223Ra and 227Th are being increasingly considered in MRT and have been investigated in this thesis through acquisition of experimental gamma-ray spectra. Monte-Carlo simulations have been developed so that modifications to the DEPICT system can be recommended for imaging radionuclides other than 131I.
Supervisor: Harkness-Brennan, Laura Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral