Dokument: Clinical Implications of Silicon Photomultiplier-based Positron Emission Tomography for Different Radionuclides
| Titel: | Clinical Implications of Silicon Photomultiplier-based Positron Emission Tomography for Different Radionuclides | |||||||
| URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=64238 | |||||||
| URN (NBN): | urn:nbn:de:hbz:061-20231218-092948-0 | |||||||
| Kollektion: | Dissertationen | |||||||
| Sprache: | Englisch | |||||||
| Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation | |||||||
| Medientyp: | Text | |||||||
| Autor: | Kersting, David Manuel [Autor] | |||||||
| Dateien: |
| |||||||
| Beitragende: | Prof. Dr. Dr. Jentzen, Walter [Betreuer/Doktorvater] Prof. Dr. Heinzel, Thomas [Gutachter] | |||||||
| Dewey Dezimal-Klassifikation: | 500 Naturwissenschaften und Mathematik » 530 Physik | |||||||
| Beschreibung: | Positron emission tomography (PET) is a medical imaging modality which plays an important role in daily clinical practice. It primarily serves as a tool for whole-body staging in oncology, utilizing various radioactively labelled tracers for distinct tumour entities. Since its introduction, PET imaging has benefited from continuous technical developments, including both new hardware components and advanced image reconstruction software. Most recently, the introduction of silicon photomultiplier-based (SiPM-based) PET detectors has led to major advancements. These exhibit, inter alia, an increased effective sensitivity and time-of-flight resolution. On the one hand, this can result in improved image quality and higher detectability. On the other hand, the PET acquisition time could be reduced while maintaining diagnostic performance. Shorter acquisition times can enhance patient comfort. Alternatively, lower levels of activity could be administered, potentially leading to substantial improvements in radiation safety for both patients and medical personnel. The aim of this thesis is to investigate the clinical implications of SiPM-based PET with a special focus on tumour lesion detectability and reductions in acquisition time for three PET tracers labelled with different radionuclides.
In the first experiments, we examined the effects of a reduced acquisition time on clinical SiPM-based PET imaging for the standard tracers 18F-FDG and 68Ga-PSMA. For 18F-FDG PET, in 20 lymphoma patients a reduction by a factor of 2.8 compared to the clinical standard was feasible without negative effects on region-based lesion detection rates and PET-based clinical scores. For 68Ga-PSMA, in 20 prostate cancer patients a reduction by a factor of 3.7 was associated with missed detection of two small lymph node metastases with low tracer uptake in two different patients. In one case, this would have resulted in under-assessment of the stage using standard clinical scoring methods, potentially affecting patient management. For both 18F-FDG and 68Ga-PSMA, image noise - as an indicator of image quality - was only slightly increased for the reduced acquisition time and image-based lesion quantification was comparable. These results indicate that the limit for reductions in acquisition time to maintain diagnostic quality for 18F and 68Ga is about 3. However, potential under-diagnosis of small and low-uptake lesions requires careful patient selection for reduced protocols. For patients with a high tumour load, a shortened acquisition time may be appropriate for follow-up scans where diagnosis does not rely on the characterisation of individual lesions. However, for primary staging evaluations or suspected recurrence cases, a standard acquisition protocol should be employed. In these clinical experiments, no direct comparison to previous-generation PET scanners were performed, as - because of the short half-lives of 18F and 68Ga (109.77 min and 67.71 min, respectively) - detectability and image quality in subsequent PET scans after single tracer administration would be influenced by decay and biological metabolism. However, this does not hold true for tracers with long half-life and slow metabolism. Therefore, we focused our next experiments on the non-standard radionuclide 124I. It is typically used for imaging of differentiated thyroid cancer but exhibits more challenging PET properties (for example, a low positron branching ratio). With a half-life of 4.2 d, 124I enables a direct comparison of different PET systems after single tracer administration. In an evaluation of 10 patients with differentiated thyroid cancer, the SiPM-based system outperformed two PET systems with detectors from previous generations (photomultiplier tubes and avalanche photodiodes) in lesion detectability and visual image quality. It almost reached the detectability results of scan with fivefold-prolonged duration on the avalanche photodiode-based system which was used as reference. Additionally detected lesions were of small sizes and low tracer uptake values indicating pronounced benefits of SiPM-based PET for metastases with these properties. To quantify these results, we performed a phantom investigation to compare the minimum detectable activity across a SiPM- and a photomultiplier tube-based PET system under defined conditions. The phantom was designed to resemble clinical differentiated thyroid cancer metastases at the lower ends of typical size and 124I activity concentration ranges. Overall, the minimum detectable activity was improved by a factor of 0.5 with pronounced benefits for small lesions. Moreover, the minimum detectable activity correlated linearly with the acquisition time. We, therefore, suggest a prolonged acquisition time for body regions which are typically affected by metastases - like the neck region in thyroid cancer patients. Finally, we investigated the impact of improved detectability on radioiodine therapy planning. In thyroid cancer patients, 124I PET can be used for pre-therapeutic dosimetry to predict response to 131I therapy. In a dosimetry model, we showed that lesions with predicted therapy response ≥4.5 mm in diameter are detectable on both systems at a standard acquisition time. Smaller lesions, however, were only detectable on the SiPM-based system. As they yet were predicted to show response to radioiodine therapy, SiPM-based PET can have beneficial effects on clinical patient and therapy management. | |||||||
| Lizenz: |  Dieses Werk ist lizenziert unter einer Creative Commons Namensnennung 4.0 International Lizenz | |||||||
| Fachbereich / Einrichtung: | Mathematisch- Naturwissenschaftliche Fakultät » WE Physik | |||||||
| Dokument erstellt am: | 18.12.2023 | |||||||
| Dateien geändert am: | 18.12.2023 | |||||||
| Promotionsantrag am: | 05.02.2023 | |||||||
| Datum der Promotion: | 01.08.2023 |
