Table 1 Inclusion and exclusion criteria of the PERYTON-trial. Patients are eligible if they meet all criteria

• Patients with prostate adenocarcinoma treated with radical prostatectomy;

• Tumour stage pT2-4, R0-1, pN0, or cN0, cNx according to the UICC TNM 2009, only with Gleason score available;

• A recent PSMA-PET scan (<  60 days) without evidence of lymph nodes or distant metastases;

• PSA progression after prostatectomy defined as two consecutive rises with the final PSA > 0.1 ng/mL or 3 consecutive rises. The first value must be measured ≥6 weeks after radical prostatectomy;

• PSA at inclusion < 1.0 ng/mL;

• WHO performance status 0–2 at inclusion;

• Age at inclusion between 18 and 80 years;

• Written (signed and dated) informed consent prior to registration.

• Prior pelvic irradiation, (chemo) hormonal therapy or orchiectomy;

• Previous or concurrent active invasive cancers, other than superficial non-melanoma skin cancers;

• Patients with positive lymph nodes or distant metastases based on the surgical specimen of lymphadenectomy or the following minimum diagnostic workup: PSMA-PET/CT scan, 60 days prior to registration;

• Double-sided metallic hip prosthesis;

• Inability or unwillingness to understand the information on trial-related topics, to give informed consent or to fill out QoL questionnaires.