68Ga-PSMA PET/CT for restaging recurrent prostate cancer: which factors are associated with PET/CT detection rate?

Abstract

To assess the association between PSA levels, PSA kinetics and other factors and a pathological ⁶⁸Ga-PSMA PET/CT scan in patients with recurrent prostate cancer (rPCa) with biochemical relapse (BR) after radical therapy. Seventy consecutive rPCA patients referred for ⁶⁸Ga-PSMA PET/CT, matching all the following criteria, were retrospectively evaluated: (a) previous radical prostatectomy or primary radiotherapy with curative intent; (b) BR or persisting high PSA levels after primary treatment; and (c) complete clinical and imaging information. The mean ± SD PSA level was 3.5 ± 5.3 ng/mL (median 1.7, range 0.2 – 32.2 ng/mL), the mean ± SD PSA doubling time (PSAdt) was 6.5 ± 5.5 months (median 5.5, range 1.3 – 31.6 months), and the mean ± SD PSA velocity was 7.9 ± 20.5 (median 2.1, range 0.2 – 147.5 ng/mL/year). Statistical analysis was performed to assess which factors were associated with the detection of rPCa on ⁶⁸Ga-PSMA PET/CT. ⁶⁸Ga-PSMA PET/CT was positive in 52 of 70 patients (74.2 %). In 30 patients (42.8 %) lesions limited to the pelvis were detected. Distant lesions were observed in 8 of patients (11.4 %). Local plus systemic lesions were detected in 14 patients (20 %). PSA level (p = 0.017) and PSAdt (p = 0.0001) were significantly different between PET-positive patients (higher PSA level, shorter PSAdt) and PET-negative patients (lower PSA, longer PSAdt). ROC analysis showed that PSAdt 6.5 months and PSA 0.83 ng/mL were optimal cut-off values. In multivariate analysis PSAdt was associated with ⁶⁸Ga-PSMA PET/CT positivity. ⁶⁸Ga-PSMA PET/CT was positive in 17 of 20 patients (85 %) with PSA The great potential of ⁶⁸Ga-PSMA PET/CT in patients with rPCa and BR was confirmed. PSA and PSAdt were valuable predictors of pathological ⁶⁸Ga-PSMA PET/CT findings.