SBRT-Based Prostate Radiotherapy (No Boost)

PRO-BOOST-N is a prospective, multicenter, randomized phase II/III clinical trial for patients with prostate cancer and pelvic lymph node involvement (cN1M0) confirmed by PSMA PET/CT, without distant metastatic disease. Patients with PSMA PET-staged node-positive prostate cancer are potentially curable, but remain at substantial risk of distant progression despite contemporary treatment with radiotherapy, long-term androgen deprivation therapy, and, when appropriate, androgen receptor pathway inhibitors. The optimal way to intensify radiotherapy to the prostate and PSMA PET-positive pelvic lymph nodes remains uncertain in the era of modern molecular imaging. All participants receive a standardized ultrahypofractionated whole-pelvis radiotherapy backbone delivered in five fractions, combined with long-term systemic therapy according to contemporary clinical practice. The study uses a 2 x 2 factorial randomized design to evaluate two treatment questions. The primary comparison evaluates whether prostate dose escalation improves metastasis-free survival compared with no additional prostate boost. Patients assigned to prostate boost receive one of three protocol-defined boost techniques: high-dose-rate brachytherapy, low-dose-rate brachytherapy, or single-fraction SBRT. If more than one prostate boost technique is available at the treating center and technically suitable for the patient, the boost technique is assigned by embedded subrandomization. The key secondary, hierarchically tested comparison evaluates nodal dose escalation by comparing two predefined dose levels to PSMA PET-positive pelvic lymph nodes. Organ-at-risk-driven nodal dose de-escalation is permitted within the higher-dose arm when required for patient safety and protocol compliance. The primary endpoint is metastasis-free survival (MFS) . Secondary endpoints include overall survival (OS), radiographic progression-free survival (rPFS), intraprostatic and regional nodal control, time to castration-resistant prostate cancer, time to next systemic therapy, treatment-related adverse events graded according to CTCAE version 6.0, and patient-reported quality of life, including urinary, bowel, sexual, and global health domains. PRO-BOOST-N aims to determine the optimal radiotherapy intensification strategy for patients with PSMA PET-staged node-positive prostate cancer by prospectively evaluating prostate-directed and nodal-directed dose escalation within a modern, standardized radiotherapy platform.