The Role of GA⁶⁸-PSMA PET/CT in Restaging of Biochemical Recurrent Prostate Cancer After Radical Prostatectomy and/or Radiotherapy
Authors: Çağlayan Ceyda Nur Dündar , Bural Gonca Gül , Boz Adil 
Published: April 2024

Introduction:
The aim of our study was to investigate the the diagnostic performance of PSMA PET/CT performed for restaging in subjects with biochemical recurrent prostate carcinoma after curative treatment either with radical prostatectomy (RP) or Radiation Treatment (RT).
Method
58 prostate cancer patients (Age 73 ± 8) with biochemical recurrent prostate carcinoma after curative Treatment (with RP or RT) who underwent Ga68-PSMA PET/CT between December 2015 and August 2022 were retrospectively analyzed. PSMA uptake levels were grouped as posivite or negative. Positive disease locations were classified as prostate/prostate bed, pelvic lymph node, abdominal lymph node, supradiaphragmatic lymph node, bone, visceral organ. SUVmax values were recorded for positive disease sites. According to PSMA PET/CT findings, the extent of disease was decided (pelvis limited and distant metastatic). Gleason score, ISUP grade (International Society of Urological Pathology)), PSA, PSAdt, PSAvelocity and pathological SUVmax values were recorded and compared in PET positive and negative subjects and also in RT and RP groups. Findings were correlated with histopathological results and /or radiological, clinical and laboratory findings.
Results
PSMA PET/CT was positive in 33 patients, negative in 25 patients. The sensitivity, specificity, positive predictive value and negative predictive value of PSMA PET/CT were calculated as 73.2%, 78.6%, 90.9%, 50%, respectively. Patient-based detection rate was found to be 57%. Detection rate was 24% when PSA level was < 1 ng/ml, 69% when PSA level was between 1–4 ng/ml and 81% when PSA level was above 4 ng/ml. A statistically significant correlation was found between Ga68-PSMA PET/CT positivity and age, Gleason score, ISUP grade and PSA level. PSA value was found to be significantly higher in PET-positive patients. The threshold value in the ROC analysis for PSA was calculated as 1.0050 ng/ml, and was statistically significant (p = 0.06).In the presence of bone involvement, Gleason score average and PSA were found to be higher. A statistically significant relationship was found between visceral involvement, supradiaphragmatic LN involvement and bone involvement and ISUP Grade categories. A statistically significant strong positive correlation was observed between PSA and bone SUVmax. PSA value was observed to be significantly higher in patients with distant metastases. It was noted that the PSAdt value was shorter, especially in cases with extensive metatatic disease. The uptake in local recurrence site was higher in subjects who had RT than in subcets with RP. No difference was noted for both groups in other metastatic disase sites.
Conclusion
Ga68-PSMA PET/CT has shown reliable performance in locating recurrence sites of prostate cancer. This performance is better when the PSA serum level is above 1 ng/mL. Ga68-PSMA PET/CT imaging should be considered and used as the first-line imaging modality for biochemical recurrence in prostate cancer patients who had curative treatment.