Background: The higher specificity of amino-acid positron emission tomography (AA-PET) in the diagnosis of\ngliomas, as well as in the differentiation between recurrence and treatment-related alterations, in comparison to\ncontrast enhancement in T1-weighted MRI was demonstrated in many studies and is the rationale for their\nimplementation into radiation oncology treatment planning. Several clinical trials have demonstrated the\nsignificant differences between AA-PET and standard MRI concerning the definition of the gross tumor volume\n(GTV). A small single-center non-randomized prospective study in patients with recurrent high grade gliomas\ntreated with stereotactic fractionated radiotherapy (SFRT) showed a significant improvement in survival when\nAA-PET was integrated in target volume delineation, in comparison to patients treated based on CT/MRI alone.\nMethods: This protocol describes a prospective, open label, randomized, multi-center phase II trial designed to\ntest if radiotherapy target volume delineation based on FET-PET leads to improvement in progression free survival (PFS)\nin patients with recurrent glioblastoma (GBM) treated with re-irradiation, compared to target volume delineation based\non T1Gd-MRI. The target sample size is 200 randomized patients with a 1:1 allocation ratio to both arms. The primary\nendpoint (PFS) is determined by serial MRI scans, supplemented by AA-PET-scans and/or biopsy/surgery if suspicious\nof progression. Secondary endpoints include overall survival (OS), locally controlled survival (time to local progression\nor death), volumetric assessment of GTV delineated by either method, topography of progression in relation to MRIor\nPET-derived target volumes, rate of long term survivors (>1 year), localization of necrosis after re-irradiation, quality\nof life (QoL) assessed by the EORTC QLQ-C15 PAL questionnaire, evaluation of safety of FET-application in AA-PET\nimaging and toxicity of re-irradiation.\nDiscussion: This is a protocol of a randomized phase II trial designed to test a new strategy of radiotherapy target\nvolume delineation for improving the outcome of patients with recurrent GBM. Moreover, the trial will help to develop a\nstandardized methodology for the integration of AA-PET and other imaging biomarkers in radiation treatment planning.
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