HypoFocal SRT Trial: Ultra-hypofractionated focal salvage radiotherapy for isolated prostate bed recurrence after radical prostatectomy; single-arm phase II study; clinical trial protocol. - Mathier E; Althaus A; Zwahlen D; Lustenberger J; Zamboglou C; De Bari B; Aebersold DM; Guckenberger M; Zilli T; Shelan M (BMJ open, 2024)