Characterisation of a Novel Radiation Detector and Demonstration of a Novel Error Detection Algorithm

Abstract

Radiation detectors play an important role in radiology departments, particularly in relation to imaging and dosimetry. The significant advances achieved in material properties and high-quality electronic systems during previous decades have led to a continual expansion of their role and usage. In turn, this has had a concomitant impact upon the rapid progress of radiation detector technologies, specifically those utilised in medical imaging and dosimetry. This thesis aims to evaluate a radiation detector for a particular function, and to assess its suitability for said function within radiology and radiotherapy departments. Two novel radiation detectors, one for low energy imaging (kV) and another for radiotherapy (MV), are named Lassena (kV) and Lassena (MV) respectively. These detectors underwent an evaluation for the first time in order to assess their performance. Lassena (kV) was assessed in terms of image resolution and noise level to obtain the detective quantum efficiency (DQE) values representing image quality. DQE (0.5) values were 0.46-0.59 for three beam energies. Lassena (MV) was evaluated regarding its dosimetric properties, including linearity based on dose rate, reproducibility, and uniformity. Lassena (MV) has a high degree of short-term reproducibility, an acceptable pixel uniformity-response at high dose rates, and acceptable linearity with a coefficient of determination (R2) of 0.8624. Lassena (kV) displayed promising results whilst Lassena (MV) exhibited high sensitivity to radiation. A Monte Carlo system consisting of a linear accelerator and radiation detector was built and calibrated in order to assess dose verification applications within radiotherapy using a radiation detector. Anatomical changes during radiation therapy (such as parotid shrinkage and sinusitis for a nasopharyngeal case) were replicated. Analysis of computational EPID images started to warn of a risk of deviation from the planned dose at -26.3% volume loss of the parotid gland. This is most likely to happen in the third week of the treatment, however, the user must be aware of the limitations present due to anatomical overlapping and gamma analysis.