The innovative value and objective of this study is to demonstrate that 18F-PSMA-11 PET / CT provides at least a non-inferior (or similar) diagnostic method in a prostate cancer patient population (with biochemical recurrence after local therapy with curative objective compared to 68Ga). -PSMA-11 PET / CT A second important objective is to investigate in a subpopulation whether 18F-PSMA-11 cannot be superior in the detection of oligo-metastatic disease, compared to 68Ga-PSMA-11.