Diagnostic Performance of PSMA-Based ¹⁸F-DCFPyL PET/CT in Prostate Cancer Patients after Definitive Treatment with PSA Level ≤0.2 ng/mL

Purpose The aim of this study was to investigate the role of 18F-DCFPyL PET/CT in the evaluation of prostate cancer (PC) patients after definitive treatment and with low-level prostate-specific antigen (PSA) level of ≤0.2 ng/mL. Patients and Methods This retrospective study was conducted in PC patients who received definitive treatments with PSA level of ≤0.2 ng/mL and underwent 18F-DCFPyL PET/CT within a 1-week interval of PSA examination, and without interval treatment change or history of other cancer. Patient and tumor characteristics at initial diagnosis, treatment regimens, and findings on 18F-DCFPyL PET/CT were collected. Patients with minimal 6-month (median, 11 months; range, 6-21 months) follow-up or definitive biopsy results of the suspected PET/CT findings were included. Imagine findings were reached with consensus among experienced board-certified nuclear medicine physicians. Comprehensive follow-up and/or biopsy results were used as definitive determination of presence or absence of disease. Comparisons between groups of positive and negative 18F-DCFPyL PET/CT were done by using descriptive statistics. Results A total of 96 18F-DCFPyL PET/CTs from 93 patients met the inclusion criteria. The median Gleason score (GS) of positive group is 8 (range, 6-10), whereas negative group is 7 (range, 6-10). The median age of positive group is 71 (range, 50-90), whereas negative group is 69 (range, 45-88). There were 49 positive (51%) and 47 negative 18F-DCFPyL PET/CTs (49%). Detection rates at PSA level of ≤0.1 and 0.2 ng/mL were 58.7% (27/46) and 44% (22/50), respectively. The scan-based sensitivity, specificity, positive predictive value, and negative predictive value are 100%, 95%, 96%, and 100% in group with PSA level of ≤0.1 ng/mL, and 100%, 97%, 95%, and 100% in group with PSA level of 0.2 ng/mL, respectively. Sites of involvement on positive 18F-DCFPyL PET/CTs were prostate bed, pelvic lymph nodes, bone, chest and supraclavicular lymph nodes, lung, and adrenal glands. The SUVmax value on positive lesions ranged from 1.9 to 141.4; the smallest positive lymph node was 0.4 cm. High GS of 8-10, known metastatic status (M1), presence of extraprostatic extension, presence of seminal vesicle invasion, and very high-risk PC are significantly associated with positive 18F-DCFPyL PET/CT results (P < 0.05). Of all analyzed treatment regimes, upfront surgery (radical prostatectomy with or without pelvic lymph node dissection) had strong correlation with negative PET/CT results (P < 0.001). If patients received ADT only, or ADT plus chemotherapy, the PET/CT results were most likely positive (P = 0.026). For other treatment regimes, there were no statistical differences between the groups (P > 0.05). Conclusions In the presence of low PSA level in PC patients after definitive treatment, 18F-DCFPyL PET/CT is most beneficial in detection of disease in patients with GS of 8 or higher at the time of diagnosis, and the ones who have history of ADT only, or ADT plus chemotherapy. There is excellent negative prediction value of 18F-DCFPyL PET/CT. However, there is no cutoff PSA level for 18F-DCFPyL PET/CT indication and no correlation between PSA level and SUVmax of positive lesions on 18F-DCFPyL PET/CT.