ALA-RDT in GBM: protocol of the phase I/II dose escalation trial of radiodynamic therapy with 5-Aminolevulinic acid in patients with recurrent glioblastoma oleh Niklas Benedikt Pepper, Hans Theodor Eich, Michael Müther, Michael Oertel, Stephan Rehn, Dorothee Cäcilia Spille, Walter Stummer