Salvage high-dose-rate brachytherapy for prostate cancer persistence after brachytherapy: repeated use of a polyethylene glycol hydrogel spacer - Hepp, Rodrigo; Eggert, Thilo; Schabl, Georg; Herberholz, Lars; Petry, Tim; Galalae, Razvan (Journal of Contemporary Brachytherapy, 2018)