Presentation Authors: Tobias Maurer*, Hamburg, Germany, Markus Kroenke, Alexander Wurzer, Kristina Schwamborn, Lena Ulbrich, Lena Jooß, Thomas Horn, Bernhard Haller, Wolfgang Weber, Hans-Jürgen Wester, Matthias Eiber, Munich, Germany
Introduction: 68Ga-prostate specific membrane antigen (PSMA) positron emission tomography (PET) has become a common method for primary staging of prostate cancer in Europe. However, 18F-labeled PSMA ligands are increasingly being used owing to their favorable half-life, large batch production and lower positron range compared with 68Ga-labeled counterparts. Radiohybrid PSMA (rhPSMA) ligands are a new class of theranostic PSMA-targeting agents that feature the fast synthesis associated with 18F while allowing labeling with radiometals. This retrospective analysis investigates the efficacy of 18F-rhPSMA7 PET for primary N-staging of prostate cancer compared with histopathological findings.
Methods: Data from 58 consecutive patients with high risk prostate cancer (defined by D&[prime]Amico) who were staged with 18F-rhPSMA7 PET/CT or PET/MRI between July 2017 and June 2018 were reviewed. All patients underwent subsequent radical prostatectomy and extended pelvic lymph node dissection. An experienced reader carried out a template-based analysis using a 5-point scale to determine the presence of lymph node metastases. This was conducted independently for both the PET and morphological datasets. Patient-level and template-based results were both compared to histopathological findings.
Results: The 58 patients had a median pre-scan PSA of 12.4 ng/mL (range, 1.2-81.6 ng/mL). The median injected activity of 18F-rhPSMA7 was 327 MBq (range, 132-410 MBq), with a median uptake time of 79.5 min (range, 60-153 min).Lymph node metastases were present in 18 patients (31.0%) located in 54 of 371 templates (14.6%). On the patient-level analysis, the sensitivity, specificity and accuracy of 18F-rhPSMA7 PETÂ were 72.2%, 92.5% and 86.2%, respectively, while those for morphological imaging were 50.0%, 72.5% and 65.5%, respectively. On a template-based analysis, the sensitivity, specificity and accuracy of 18F-rhPSMA7 PET were 51.9%, 96.6% and 91.4%, respectively and those for morphological imaging were 11.1%, 95.3% and 84.1%, respectively. ROC analyses indicated that 18F-rhPSMA7 PET performed significantly better than morphological imaging on both the patient and template-based analyses (AUCs: 0.858 vs. 0.649 [p = 0.012] and 0.753 vs. 0.594 [p = 0.035], respectively).
Conclusions: 18F-rhPSMA7 PET is superior to morphological imaging for N-staging of primary high risk prostate cancer. The efficacy of 18F-rhPSMA7 PET is in the same range as that previously reported in the literature for 68Ga-PSMA11.