⁶⁸Ga-PSMA-PET/CT after a non-contributively ¹⁸F-Choline PET/CT in patients in biochemical relapse of prostate cancer

Introduction: PSMA PET/CT is a recent nuclear medicine exam, particularly useful in the management of patients followed for prostate cancer. The aim of this study was to establish the detection rate of PSMA-PET/CT after a non-contributively ¹⁸F-Choline PET/CT in patients in biochemical relapse of prostate cancer.

Material and Methods: From July 2017 to April 2019, 120 consecutive patients (mean age: 71.2 years old ± 6.6) underwent ⁶⁸Ga-PSMA-PET/CT in our centre, at maximum 3 months after a non-contributively ¹⁸F-Choline PET/CT. All of them were in biochemical relapse after curative therapy (prostatectomy and/or radiotherapy and/or brachytherapy). Images were analysed visually in order to localise the recurrence. Findings on ⁶⁸Ga-PSMA-PET/CT were correlated with PSA level for different thresholds (3 groups: group 1, PSA ≤0.5 ng/ml; group 2, 0.5<PSA ≤ 1.0 ng/ml and group 3 PSA > 1.0 ng/ml) and initial treatment (prostate surgery vs other).

Results: Mean PSA level was 5.9 ng/ml (± 13.2). Overall, ⁶⁸Ga-PSMA-PET/CT localized recurrence contributing positively in the diagnostic thinking in 93 cases for an overall detection rate of 77.5% (93/120). In 24 patients the contribute of ⁶⁸Ga-PSMA-PET/CT was considered insignificant, while for 3 cases it was not possible to determine the impact of ⁶⁸Ga-PSMA-PET/CT over ¹⁸F-Choline PET/CT. Noteworthy, in none ⁶⁸Ga-PSMA-PET/CT was considered source of error. In group 1 ⁶⁸Ga-PSMA-PET/CT contributed positively in 43.5% (7/16), in group 2 ⁶⁸Ga-PSMA-PET/CT contributed positively in 93% (13/14) and in group 3 ⁶⁸Ga-PSMA-PET/CT contributed positively in 81% (73/90). ⁶⁸Ga-PSMA-PET/CT showed a higher detection rate in group 2 compared to 1 (p= 0.007) as well as in group 3 compared to 1 (p=0.001), while no significant difference was seen between groups 2 and 3 (p=0.28). Among 59 patients previously treated by prostatectomy ⁶⁸Ga-PSMA-PET/CT contributed positively in 43, while among 61 patients not previously treated by prostatectomy ⁶⁸Ga-PSMA-PET/CT contributed positively in 50, p=0.23.

Conclusions: In biochemical relapse, patients with a non-contributively Choline PET/CT should undergo PSMA-PET/CT given its high detection rate, although depending from PSA. To date, more and more data leads to replace Choline PET/CT by PSMA-PET/CT in the management of patients followed for prostate cancer.