Assessment of 18FLT PET-CT for Volume Definition of High-grade Gliomas (GLIO-TEP)

18F-Fluorothymidine is a recently developed PET tracer to image tumor cell proliferation. Very few data report an interest of using such a tracer for cerebral malignant tumor management. In our project, we want to compare the tumoral volumes obtained with PET and MRI, with the gold standard histopathological diagnosis according to the WHO grading malignancy scale and the Ki-67 proliferation index, for preoperative evaluation as much as for tumoral postoperative residue evaluation. Furthermore, we want to explore the interest of 18F-FLT-PET volume to better delineate tumoral volume in radiotherapeutic management of gliomas.

* Background: 18FDG is the most widely used tracer for oncologic positron emission tomography (PET). However, the high glucose utilization of normal gray matter limits its utility in brain explorations. More recently, 18FLT was introduced as a PET tracer for tumor imaging. It has been found useful for non-invasive assessment of the proliferation status of various tumors. Its potential clinical use in the evaluation of brain tumors has not been clearly determined because of sparse studies. * The primary objective of this study is to assess the positive predictive value of PET-CT uptake of 18FLT in diagnosing malignant tissue by comparison with the histopathological gold standard diagnosis according to the WHO grading malignancy scale and the Ki-67 proliferation index, at the time of preoperative evaluation. * Secondary objectives are: to describe and compare preoperative tumor volumes and postoperative residual tumor volumes as assessed by 18FLT PET-CT and MRI, and to describe a quantitative proliferation index with PET (SUV for "standardized uptake value"). * Study design: This is an exploratory cross-sectional study at two separate times: pre-and postoperative. Eligible patients will be included consecutively. Histological samples will be analyzed blindly to imaging data. Assessments of PET-CT and MRI volumes will be blind to each other. * Procedure: After information and written informed consent and before surgery, patients will undergo MRI and 18F-FLT PET-CT to obtain the tumor volume according to both modalities. Then, surgeons will make different biopsies from i) areas with MR abnormalities and FLT uptake, ii) area with FLT uptake and no MR abnormality (on the surgery approach way or in not functional areas), iii) area with MR abnormality without any FLT uptake, iiii) area without any uptake where biopsy is possible because the area is on the surgery approach way. Then, the samples will be blindly analyzed to determine the Ki-67 proliferation index and WHO grading malignancy scale. Patients will undergo again 18F-FLT PET-TDM and MRI at least 4 weeks after surgery, in the week preceding radiotherapy, to determine residual tumor volumes.