Molecular Imaging with 18F-PSMA-1007 PET/CT in Multimodal Evaluation of Recurrence of Prostate Cancer

Purpose: According to American Cancer Society, 1 man in 9 has the probability of getting diagnosed with prostate cancer (PCa) in their lifetime. 1 out of 41 men dies due to prostate cancer every year [1]. The main radical treatment methods of prostate cancer are surgery and radiation therapy. In patients with clinically intermediate/high risk prostate cancer after initially radical treatment recurrences occur, therefore further treatment requires imaging of precise volume and localization of recurrent disease. Recurrence of prostate cancer can be assessed by magnetic resonance imaging (MRI) and positron emission tomography (PET/CT). Radiopharmaceutical 18F-PSMA-1007 is a ligand, used in PET/CT and it has some advantageous characteristics in recurrent prostate cancer diagnostics, even in comparison to 68Ga-PSMA ligand [2]. Low urinary background clearance of 18F-PSMA-1007 provides higher diagnostic value of PET/CT in evaluation of the prostate bed and pelvis in recurrent PCa patients [3]. The aim of this study was to compare the diagnostic tools - 18F-PSMA-1007 PET/CT and MRI for evaluation of local recurrence and regional lymph nodes. Methods and materials: This comparative prospective study included 29 prostate cancer patients with biochemical relapse referred for 18F-PSMA PET/CT, who were previously treated with radical prostatectomy and/or radiation therapy of the prostate bed. The results of MRI and PET/CT were compared using a reference standard that was based on clinical data of patients and/or follow-up information. According to the reference standard all results of examinations were classified as true positive, false positive, true negative or false negative. The diagnostic sensitivity, specificity, accuracy, positive predictive value (PPV) and negative predictive value (NPV) of both methods - 18F-PSMA-1007 PET/CT and MRI - of the prostate cancer biochemical recurrence was studied. Results: 29 patients with biochemical prostate cancer recurrence were prospectively enrolled into the study (mean age: 66.83± 6.76 (range 52 – 84) years). Mean PSA value at the time of the studies were 2.48 ng/ml, median Gleason score was 7 (range 5-9), PSA median doubling time 3.9 months.
The evaluation of local recurrence was based on results of PET/CT and MRI. In our study this included a pathologic 18F-PSMA-1007 uptake in the prostate or prostate bed as reported in 10/29 patients (35 %). In MRI prostate cancer recurrence was documented on 9/29 scans (31%). The mean SUVmax value of recurrent local lesions in PET/CT was 6.9. Against the standard of reference, sensitivity, specificity, accuracy, PPV and NPV for 18F-PSMA-1007 PET/CT were 90.9%, 100%, 96.5%, 100% and 94.7% and for MRI - 81.8%, 100%, 93.1%, 100% and 90.0%, respectively. Regional lymph nodes were detected more accurately by PET/CT in 48% (n=14/29) patients, while 28% of lymph node metastases were detected on MRI (n=8/29). All of the metastatic lymph nodes were smaller than 1 cm in short axis (mean short axis 0.73 cm). Sensitivity, specificity, accuracy, PPV and NPV for 18F-PSMA-1007 PET/CT were 92.9%, 93.3%, 93.1%, 92.9%, 93.3% and MRI - 57.1%, 100%, 79.3%, 100%, 71.4%, respectively. Conclusion: This study results revealed 18F-PSMA-1007 PET/CT as superior diagnostic tool to MRI for evaluation of prostate cancer local recurrence and lymph node metastases. Both methods detect recurrence with high accuracy, but 18F-PSMA-1007 PET/CT showed better detection of recurrence in small size lymph nodes with non-specific characteristics on MRI.