Trial of Ultrahypofractionated Focal Salvage Radiotherapy for Isolated Prostate Bed Recurrence After Radical Prostatectomy (HypoFocal SRT)

Inclusion Criteria: Written informed consent according to ICH/GCP (International Council for Harmonisation/Good Clinical Practice) regulations before registration and prior to any trial specific procedures Age ≥ 18 years at time of registration WHO performance status 0-1 Lymph node negative adenocarcinoma of the prostate treated with radical prostatectomy (RP) at least 6 months before trial Tumor stage pT2a-3b, R0-1, pN0 or cN0 according to the Union for International Cancer Control (UICC) TNM 2009. Evidence of measurable local recurrence at the prostate bed detected by PSMA PET/CT and mpMRI within the last 3 months. In case of unclear local recurrence, a biopsy confirmation is recommended. Patient must have non-metastatic (N0, M0) disease, as defined by a lack of nodal or distant metastases seen on PSMA PET/CT scan Patients must have non-castrate levels of serum testosterone (≥50 ng/dL). Patients must not have previously received hormonal therapy (LHRH agonists, antiandrogen, or both, or bilateral orchiectomy). Absence of any psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule; those conditions should be discussed with the patient before registration in the trial Exclusion Criteria: Persistent PSA (> 0.4 ng/mL) 4 to 20 weeks after RP Previous hematologic or primary solid malignancy within 3 years prior registration with the exception of curatively treated localized non-melanoma skin cancer Usage of products known to affect PSA levels within 4 weeks prior to start of trial treatment phase including any form of androgen suppression agents and androgen deprivation therapy Bilateral hip prosthesis Severe or active co-morbidity likely to impact on the advisability of SRT Treatment with any experimental drug or participation within a clinical trial within 30 days prior to registration (exception: concurrent participation in the biobank studies is allowed)