https://www.um.edu.mt/library/oar/handle/123456789/2296 2026-04-15T09:51:39Z https://www.um.edu.mt/library/oar/handle/123456789/2788 Title: Repeatability of ejection fraction and left ventricular volume measurement from gated SPECT : using a solid-state CZT gamma camera Abstract: Background: Many patients undergoing cardiotoxic chemotherapy or with cardiac diseases require re-assessment of left ventricular ejection fraction, and it is important that the test used shows good repeatability. Objectives: The objective of this study was to assess the short-term repeatability of serial re-acquisitions of ejection fraction and volumes from gated single photon emission computed tomography using Quantitative Gated SPECT software and a Discovery NM 530c solid-state gamma camera. Research Design: This study involved retrospective data analysis from 200 patients who had undergone routine repeat Tc-99m tetrofosmin gated SPECT. The patient sample consisted of an equal number of male and female patients and excluded studies with low count rates and small end-diastolic volume (<50 ml). Two successive gated perfusion images had been acquired at rest in the supine position at 45-minutes post injection on the solid-state gamma camera with 10-30 minutes between studies. The standard injected activity was 550 MBq. Results: For the whole population group, there was no clinically significant difference for the ejection fraction (8.9%) between initial and repeat measurements (M = 63%, SD = 12% and M = 59.5%, SD = 13%). The absolute mean difference was 3.8% (SD = 2.83%) for a range of 15 - 88%. The differences in ejection fraction and volumes are similar to previous studies. No significant differences were found between the ejection fraction differences of repeat measurements between groups of age, body mass index, sex and normal/reduced ejection fraction. Conclusions: Results demonstrate comparable repeatability to that from radionuclide ventriculography, indicating that gated single photon emission computed tomography can be used for serial assessment of ejection fraction as an alternative to radionuclide ventriculography. Recommendations: It is recommended that radiographers be properly trained for manual processing when reconstructing the studies in order to minimize errors. As for future work it is suggested that long-term re-acquisitions are compared using a larger sample. 2014-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/2564 Title: Development of a planning class solution for VMAT treatment of anal cancer Abstract: Anal cancer target volumes are large and complex when organs at risk (OAR) are to be spared. Volumetric modulated arc therapy (VMAT) is a state of the art technique that should produce a significant improvement in OAR shielding compared to 3D conformal radiotherapy (3D-CRT). The purpose of this study was to develop a clinically acceptable VMAT planning class solution for anal cancer patients which is preferable to the present 3DCRT in terms of dose conformity and organ at risk sparing. A VMAT planning class solution was developed using a suitable treatment planning system (TPS). The study was based on retrospective CT datasets of 6 anal cancer patients who had been already treated with 3D-CRT; five patients were staged T1-T2/N0 and one patient T3-T4/N1. Three VMAT plans were generated for each patient using the class solution; a double arc plan with a flattening-filter beam (FF), a double arc plan with flattening-filter free (FFF) beam and a single arc plan (SA). The three plans generated for each patient were compared in terms of the dose conformity, homogeneity, target coverage, organs at risk sparing, monitor units per fraction (MU), treatment time (TTT) and number of segments (NS). The three investigated VMAT treatment techniques produced similar target conformity but offered significant improvement in OAR sparing compared to 3DCRT. The double arc VMAT plans achieved similar target coverage as the SA plan but were statistically significantly better in terms of organs at risk sparing, particularly in sparing the small bowel, femoral heads, bladder and healthy tissue. Mean and Standard Error of Mean TTT, MUs and NS for the FF beam were 233±23s/808±92/136±6; that of the FFF beam 179±25 s/960±156/151±5 and that of the SA plan 193±7 s/1096±72/148±7. The VMAT clinical plans offer a significant improvement over 3D-CRT plans in terms of dose conformity and organs at risk sparing. This should produce less radiation-related toxicity. Double arc VMAT is the recommended treatment modality. The use of a FFF beam reduces treatment time significantly and produces similar dosimetric results as a FF beam. 2014-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/2554 Title: In-Vivo Dosimetry for HDR Prostate Brachytherapy Abstract: The main challenge in radiotherapy is to accurately deliver a prescribed radiation dose to the tumour while limiting the dose to surrounding healthy organs and tissues. The ultimate quality assurance would be the use of an online in-vivo dosimetry system, which would verify the dose delivered to the patient in real-time while treatment is delivered. Furthermore, in-vivo dosimetry measurements could be compared to the treatment planning system. The dosimeter used for this study was the Metal-oxide semiconductor field-effect transistor because of its several advantages. The main objective was to develop a real-time in-vivo dosimeter service for High Dose Rate prostate brachytherapy. This study involved commissioning and calibrating the dosimeter for use in High Dose Rate prostate brachytherapy. Tests included linearity, calibration, consistency and reproducibility, anisotropy (azimuthal and polar), temperature dependence and energy dependence. Six treatment plans created on a phantom meeting clinical guidelines were created using the treatment planning system under ultrasound guidance and these were used to first generate the correction factors required to produce the predicted voltage to the dosimeter, and finally assessing three of the six plans in real-time. The dosimeter responds linearly with dose, over the clinical dose range (0.01 Gy to 20 Gy), with R2= 0.9991. Anisotropy azimuthal and polar resulted in a minimal dependence within the uncertainty of the measurements; hence no azimuthal and polar correction factors were applied to phantom measurements. The dosimeter is energy dependent hence; a distance dependent energy correction factor was applied to treatment planning system values to produce the predicted value. An average of the calibration correction factors was also applied to the treatment planning system values to convert the dose (Gy) to (mV). Temperature was found to be dependent with a percentage difference of 7% between calibration temperature and body temperature. The measured phantom plans (mV) were in good agreement with the predicted voltage of the dosimeter (mV). The maximum percentage differences between the measured and the predicted was of 5.082%. Clinical plans in real-time were analysed and found that this is an optimal way to detect gross errors per individual needles. Total uncertainty budget of this study was 9.97% for k=2. In-vivo dosimetry in brachytherapy is currently not well established in clinical routine use to detect errors; hence, implementing this dosimeter is the way forward to start verifying treatments and therefore being capable of detecting gross errors. 2014-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/2551 Title: An implementation of a quality assurance method using a cylindrical 68GE Phantom for measuring spatial resolution in PET Abstract: Background: Important information regarding spatial resolution can be ob- tained from the daily uniformity quality control test performed on a Positron Emission Tomography (PET) scanner using a cylindrical 68Ge phantom. This information can be used to assess scanner spatial resolution over time and to pro- vide multicenter clinical trials with further data for comparing scanners to ensure inter-center image quality. Objectives: To compare two methods for obtaining spatial resolution estimates from the daily uniformity quality control image of a cylindrical 68Ge phantom and to investigate the short and long term repeatability and robustness to small changes in acquisition and reconstruction parameters. Research Design: The value of spatial resolution obtained for each of two scanners (GE Discovery 690 and Philips Gemini TF) using the NEMA NU2 (2007) protocol was used as a reference value for comparison to those obtained from the trial methods. Of the two methods investigated, one included applying Fourier analysis to a transaxial image of the cylindrical 68Ge phantom, and the other applying an edge spread function to a coronal image slice from the same phantom acquisition. Results and Conclusions: Using the Discovery 690's daily quality control pa- rameters, the Fourier analysis method gave a spatial resolution estimate of 5.39 0.09 mm, whilst the edge spread function method gave 9.67 0.47 mm. Both methods were found to be repeatable and robust. They were also found to be sensitive to changes in acquisition and reconstruction parameters, and degrada- tion in scanner spatial resolution. The Fourier analysis technique was found to be independent of position in the FOV, and dependent on count density. 2014-01-01T00:00:00Z