RIsk aDapted Stereotactic Radiotherapy vs. standarD of Care Radiotherapy in Patients With Prostate Cancer in the Adjuvant or saLvage sEtting With or Without Lymph Node Irradiation (RIDDLELN) - A Phase III Trial

The goal of this clinical trial is to determine whether stereotactic body radiotherapy (SBRT) delivered in five fractions is non-inferior to standard-of-care mildly hypofractionated radiotherapy in terms of patient-reported quality of life in adults with prostate cancer who require adjuvant or salvage radiotherapy after radical prostatectomy. The trial includes patients with or without a macroscopic recurrence in the prostate bed and allows irradiation of the regional lymphatic drainage when clinically indicated. The main questions it aims to answer are: * Is SBRT non-inferior to standard-of-care radiotherapy regarding urinary (GU) quality of life, measured by the change in the EPIC-26 GU domain score from baseline to 24 months after radiotherapy? * Is SBRT non-inferior to standard-of-care radiotherapy regarding bowel (GI) quality of life, measured by the change in the EPIC-26 GI domain score from baseline to 24 months after radiotherapy? Researchers will compare SBRT delivered as 6 Gy × 5 fractions to the prostate bed with standard-of-care radiotherapy delivered as 2.625 Gy × 20 fractions (total dose 52.5 Gy) to determine whether the substantially shorter SBRT treatment provides non-inferior patient-reported urinary and bowel outcomes. When clinically indicated, treatment of the lymphatic drainage and a simultaneous integrated boost to macroscopic recurrence or involved lymph nodes may also be delivered. Participants will: * Be randomly assigned in a 1:1 ratio to receive either five-fraction SBRT or 20-fraction standard-of-care radiotherapy. * Receive radiotherapy to the prostate bed, with additional irradiation of the regional lymphatic drainage and/or a boost to macroscopic disease or involved lymph nodes when clinically indicated. * Complete questionnaires assessing quality of life, urinary symptoms, and sexual function, including EPIC-26, IPSS, and IIEF-5. * Undergo clinical assessments, PSA measurements, assessment of treatment-related adverse events, and radiological imaging when clinically indicated. * Attend follow-up assessments at 3, 6, 12, 18, and 24 months after radiotherapy and then annually for up to 5 years. A total of 206 participants are planned for the trial. In addition to the primary quality-of-life outcomes, researchers will assess acute and late toxicity, biochemical recurrence-free survival, progression-free survival, time to further anti-cancer therapy, prostate cancer-specific survival, and overall survival.

Sex

Male

Minimum age

18 Years

Inclusion Criteria:

* Confirmed prostate cancer treated with radical prostatectomy (≥ 6 months since radical prostatectomy)
* Indication for adjuvant or salvage radiotherapy (e.g. persisting or rising PSA, macroscopic recurrence, R1 resection, pT3b) at the discretion of the treating physician
* Androgen deprivation therapy allowed at the discretion of the treating physician
* WHO performance status 0-1
* Age ≥ 18 years
* Indication for treatment of the locoregional lymphatic drainage at the discretion of the treating physician allowed (not mandatory)
* Personally signed and dated written informed consent

Exclusion Criteria:

* Inability to follow the procedures of the study (e.g. due to language problems, psychological disorders, dementia)
* Comorbidities which predispose to significant radiotherapy toxicities (e.g. inflammatory bowel disease), at the discretion of the treating physician
* Prior radiotherapy to the intended treatment site
* Presence of distant metastases (M1a is not an exclusion criterion)