Weekly Online CT or MR Adaptive Definitive SBRT for Very High Risk Localized or Regionally Metastatic Prostate Cancer

This interventional prospective multicenter international study will include 54 patients with very high-risk localized (cN0 cM0) or regional (i.e. cN1 cM0) prostate cancer according the NCCN criteria. Patients will be treated with weekly CT or MR-informed online adaptive SBRT of the prostate and elective pelvic lymph nodes with 5 x 5 Gy. In the case of regional lymph nodes, a simultaneous integrated boost (SIB) of involved lymph nodes will be performed with 5 x 6.5 Gy. In the case of up to 2 dominant intraprostatic lesion (DIL) a SIB of the DIL with 5 x 9 Gy can be performed (optional). Importantly, coverage of these DIL volumes must be compromised as needed to respect OAR constraints. This study is classified as risk category A according to ClinO, Art. 61, as stereotactic radiotherapy (SBRT) for localized or regional prostate cancer has been extensively evaluated in prospective interventional trials and is considered an established therapeutic modality. Weekly CT- or MR-guided online adaptive SBRT to the prostate and elective pelvic lymph nodes with 5 × 5 Gy is, however, not yet routinely implemented for this specific patient population. A diagnostic high field MRI during radiotherapy, e.g. week 3 is optional. Follow-up is also according to standard of care (except for patient reported outcome measure using QLQ-C30 and QLQ-PR25 and a diagnostic MRI at 9 months after SBRT (optional), and 12 months in the case of an image non-complete response at 9 months (optional).