Inclusion Criteria:  PSA-relapse, defined as PSA at 0.02 - 1.5 ng/ml after radical prostatectomy A PSA doubling time of > 6 months PSMA PET-CT positivity with a maximum of three lymph node lesions (para-aortic, iliac or obturator nodes) with or without prostate bed involvement Salvage radiotherapy planned without androgen deprivation treatment  Exclusion Criteria:  Chronic inflammatory bowel disease Bone metastases due to prostate cancer