| dc.description.abstract | Prostate cancer is the most commonly diagnosed cancer in men. In the Norwegian population, it is expected that as many as one in nine men will develop prostate cancer by the age of 75. Through early detection and effective treatment, the prognosis of patients diagnosed with prostate cancer is generally quite good and has improved in recent years. However, as many as 25% of patients will eventually develop biochemical recurrence after initial treatment with curative intent.
The emergence of prostate-specific membrane antigen (PSMA) PET in the early 2010s revolutionized the role of nuclear medicine in the management of prostate cancer recurrence. PSMA PET has been shown to outperform conventional imaging modalities like MRI, CT and bone scintigraphy for detection of recurrence and has been shown to change clinical management in as many as 50% of patients.
The combination of the hybrid PET/MRI scanner with PSMA tracers was seen as a potential one-stop shop for detection of biochemically recurrent prostate cancer. The modality combines the excellent soft-tissue contrast of MRI in the prostate bed with the excellent performance of PET to detect spread to regional lymph nodes and distant metastases. Despite these initial promises, the adoption of PET/MRI in clinical practice for prostate cancer has been relatively slow. This slow adoption rate can be attributed to factors like the high investment cost and the maturity of the technology itself. Consequently, the role of PET/MRI in clinical practice for patients with prostate cancer has yet to be fully defined.
In this thesis, we investigated the role of PET/MRI in prostate cancer with a particular focus on the role of 18F-PSMA-1007 PET/MRI in biochemical recurrence. The thesis is based on three papers. In Paper I we examined the added benefit of 18F-PSMA-1007 PET to conventional imaging, and whether the origin of the PET images, that is whether they were acquired with a PET/MRI or PET/CT scanner, has an impact on detection rate, staging and subsequent clinical management. Our results indicated a similar performance for PET/CT and PET/MRI. We also found that the addition of PSMA PET (from either PET/MRI or PET/CT) to conventional imaging improved reader agreement in staging and changed the intended treatment plan in more than 40% of patients.
In Paper II, we established normal ranges for reference tissue uptake in 18FPSMA-1007 PET. Current clinical guidelines for PSMA PET interpretation stratify lesion uptake using a PSMA expression score, which expresses the uptake in the lesions relative to the uptake in select reference tissues. We found that this expression score might not be appropriate for a considerable number of patients examined with 18F-PSMA-1007. Consequently, the current clinical guidelines may need to be adapted to more accurately account for the difference in uptake patterns of 18F-PSMA-1007 compared to tracers like 68Ga-PSMA-11 and 18F – DCFPyl.
In Paper III, we investigated one of the remaining technical challenges in PET/MRI, namely attenuation correction. We proposed a novel deep learningbased solution to include bone information in PET/MRI attenuation correction and showed that the model outperforms the current clinically available attenuation correction methods for pelvic PET/MRI examinations.
In summary, this thesis examined the current role of PET/MRI in prostate cancer, with a specific emphasis on 18F-PSMA-1007 PET/MRI for biochemical recurrence. We compared PET/MRI to imaging with PET/CT and multiparametric MRI to investigate differences in lesion detectability, staging, and subsequent impact on clinical management. We established a normal range for reference tissue uptake for 18F-PSMA-1007 PET and considered how the difference in uptake patterns might influence the reporting of findings compared to 68Ga-PSMA-11 PET.We also proposed a novel attenuation correction method that provides more quantitatively accurate images than with current clinically available methods. Collectively, these contributions in the field of PSMA PET imaging may benefit prostate cancer patients in the long term. | en_US |
