https://www.um.edu.mt/library/oar/handle/123456789/130903 Fri, 12 Jun 2026 12:29:25 GMT 2026-06-12T12:29:25Z https://www.um.edu.mt/library/oar/handle/123456789/131340 Title: Class solution development for volumetric modulated arc therapy planning of cervical cancer and the investigation of source-to-skin distance changes during radiotherapy treatment Abstract: Background: Cervical cancer continues to be a leading cause of morbidity and mortality worldwide. Advancements in radiotherapy, particularly volumetric modulated arc therapy, reduces treatment-related toxicity by providing highly conformal dose distributions. The implementation of class solutions facilitates consistent and efficient treatment planning, essential for optimising patient outcomes. Patient’s anatomy may also change during radiotherapy, which can alter source-to-skin distances, affecting dose distributions and necessitating adjustments in treatment plans. Current practices in Malta reassess treatment plans if monitor unit variations exceed ± 2 % due to source-to-skin distance changes, although this threshold lacks scientific evidence. Objectives The study aimed to develop a generalisable volumetric modulated arc therapy treatment planning class solution for cervical cancer which complies with the national clinical protocol based on the EMBRACE II studies, and to facilitate future treatment planning. In addition, it aimed to investigate the dosimetric effects of source-to-skin distance changes in cervical cancer patients by applying different margin adjustments to establish an evidence-based threshold for when a monitor unit adjustment is required. Research Methodology: The research methodology was quantitative, focusing on data analysis from the optimisation and validation of the volumetric modulated arc therapy class solution and examining absorbed dose variations after applying source-to-skin distance margins of different sizes and directions. An experimental and comparative approach was used to develop a generalisable class solution and investigate the effects of source-to-skin distance changes mimicking patient anatomical fluctuations. CT scans from 20 cervical cancer patients prescribed 45 Gy in 25 fractions were used, together with the Monaco® Treatment Planning System v5.11.03 and the Monte Carlo algorithm as the data collection tools. Results: The class solution achieved a 97.48 % pass rate for hard dose constraints and 46.30 % for soft dose constraints, suggesting it provides a good foundation but requires further patient-specific optimisation. Significant changes in dose distributions were observed with the smallest margin changes (± 0.5 cm), indicating that even minor modifications in treatment plans may require monitor unit adjustment. Conclusions and Recommendations: The study successfully developed a generalisable volumetric modulated arc therapy class solution for cervical cancer that adhered to the national clinical protocol. A revised monitor unit percentage difference threshold of 1.4 ± 0.4 % was also established, serving as an evidence-based clinical recommendation. Description: M.Sc. Med.Phy.(Melit.) Mon, 01 Jan 2024 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/131340 2024-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/131285 Title: Design and fabrication of an anthropomorphic 3D printed thoracic phantom for MyoSPECT validation in obesity imaging Abstract: Introduction: The primary aim of this study was to create a custom 3D-printed phantom and evaluate the MyoSPECT Myocardial Perfusion Imaging (MPI) system’s ability to image morbidly obese patients. Additionally, the study investigated the use of various fat-tissue replication materials, including Polylactic Acid (PLA) and gelatin-based mixtures, in imaging applications. Methodology: A 3D-printed thoracic anthropomorphic phantom was designed and fabricated to represent a patient with Body Mass Index (BMI) of 45kg/m2. The phantom was developed using a 10% lightning infill, chosen to ensure structural integrity while maintaining anatomical realism. The performance of the MyoSPECT was explored by testing the imaging in both supine and prone positions. Results: The results confirmed that the extended Field of View (FOV) of the MyoSPECT was not sufficient to fully image the left ventricle within the phantom, particularly in the supine position. Prone imaging offered slightly better image uniformity and coverage of the left ventricle, however, some areas of the phantom remained incompletely imaged. In contrast, imaging with conventional Single-photon emission computed tomography (SPECT)/CT provided complete coverage and uniformity, confirming the challenges that MyoSPECT faces when imaging larger patients. The study also explored the use of PLA and gelatin as potential fat-tissue replication materials. Although they could not be directly applied to the printed model, both materials were tested separately for their Hounsfield Unit (HU) values. The results showed that PLA with an 80% infill closely replicates the HU values of adipose tissue, while a 6% gelatin mixture also provided promising results. Conclusion: This research shows that 3D-printed phantoms can be used effectively to investigate performance of imaging systems. The MyoSPECT is unable to adequately image patients with Body Mass Index (BMI) of 45kg/m2 and over. Future research is needed to refine phantom designs and determine the exact cut-off patient dimensions for extended FOV systems. Description: M.Sc. Med.Phy.(Melit.) Mon, 01 Jan 2024 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/131285 2024-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/131284 Title: Investigation of the effect of different functional MRI sequences on local homogeneity measures : implications for neuroimaging studies Abstract: Background: Data analysis in functional magnetic resonance imaging (fMRI) is typically performed using model-based methods such as the general linear model, whose detection power is limited by the models’ complexity. The field of fMRI has started adopting data driven approaches. This includes the Vogt-Bailey index, which has not been tested across pulse sequences. Objectives: The study aimed to assess functional activation in fMRI across pulse sequences using the Vogt-Bailey index, and benchmark the results against the general linear model. Methodology: A cohort of 10 research volunteers were scanned in a 3T magnetic resonance imaging (MRI) scanner using 3 separate pulse sequences employing voxels of volumes 1.83mm3 , 23mm3 , and 2.53mm3 respectively while performing a block-design finger tapping experiment. The data was analysed with the Vogt-Bailey index and the general linear model. The brain activation maps obtained for each sequence were compared using the Dice-Sørensen coefficient, and the results from the two techniques were compared using the Overlap coefficient. Results: Applying the Vogt-Bailey index on spatially smoothened data enhanced conformance to the general linear model, with moderately-high Overlap coefficients (0.4 to 0.7). Applying the Vogt-Bailey index on unsmoothened data produced more specific results, exhibiting less conformance to the general linear model, with low-moderate Overlap coefficients (0.2 to 0.3). The functional activation detected by the general linear model was only a subset of that detected with the Vogt-Bailey index. Overall, the results of the general linear model were more reproducible across sequences with moderately-high Dice coefficients (0.6 to 0.7). Conclusions and Recommendations: Spatial smoothing of the 2.53mm3 data may be applied prior to the Vogt-Bailey analysis for higher conformance to the general linear model. Alternatively, for somatotopic evaluations, the Vogt-Bailey analysis may be applied on unsmoothened higher resolution data. The results require further validation across a larger cohort of subjects. Description: M.Sc. Med.Phy.(Melit.) Mon, 01 Jan 2024 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/131284 2024-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/131254 Title: Design and fabrication of a 3D-printed anthropomorphic heart model to investigate myocardial perfusion Abstract: Background: The demand for custom medical phantoms has driven advancements in 3D-printing within nuclear medicine. This study focused on fabricating a 3D-printed anthropomorphic left ventricular heart phantom for myocardial perfusion imaging (MPI) and evaluating its performance on SPECT and MyoSPECT systems. Objectives: The main objectives were: (1) Identify optimal 3D-printing materials/parameters for a waterproof phantom, (2) Compare MyoSPECT and traditional SPECT imaging, and (3) Assess the best dose protocols for clinical imaging. Research Methodology: A heart phantom was designed using Fused deposition modeling (FDM) with PETG, postprocessed for waterproofing, and imaged with SPECT/MyoSPECT at varying doses. Statistical analysis was performed to compare imaging quality. Results: The study found that PETG provided the best results for producing watertight phantoms. The MyoSPECT system outperformed conventional SPECT, particularly at lower doses, showing superior imaging quality and defect detectability. Statistical analysis also revealed differences in certain heart segments Conclusions and Recommendations: This study demonstrates the potential of 3D-printed phantoms in nuclear medicine. MyoSPECT offers better imaging. Recommendations include integrating 3D printing for personalized phantoms and optimizing dose protocols. Future research should explore advanced 3D-printing methods and thoracic phantom simulations. Description: M.Sc. Med.Phy.(Melit.) Mon, 01 Jan 2024 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/131254 2024-01-01T00:00:00Z