Brain tumors.

For most cancers, PET is essentially a diagnostic tool. For brain tumors, PET has got its main contribution at the level of the therapeutic management. Indeed, specific reasons render the therapeutic management of brain tumors, especially gliomas, a real challenge. Although some gliomas may appear well-delineated on conventional neuroimaging such as CT and MRI, they are by nature infiltrating neoplasms and the interface between tumor and normal brain tissue may not be accurately defined. Moreover, gliomas may present as ill-defined lesions for which various MRI sequences combination does not provide a unique contour for tumor delineation. Also, gliomas are often histologically heterogeneous with anaplastic areas evolving within a low-grade tumor, and contrast-enhancement on CT or MRI does not represent a good marker for anaplastic tissue detection. Finally, assessment of tumor residue, recurrence, or progression, may be altered by different signals related to inflammation or adjuvant therapies, and contrast enhancement on CT and MRI is not an appropriate marker at the postoperative or posttherapeutic stage. These limitations of conventional neuroimaging in detecting tumor tissue, delineating tumor extent and evidencing anaplastic changes, lead to potential inaccuracy in lesion targeting at different steps of the management (diagnostic, surgical, postoperative, and posttherapeutic stages). Molecular information provided by PET has proved helpful to supplement morphological imaging data in this context. F-18 FDG and amino-acid tracers such as C-11 methionine (C-11 MET) provide complementary metabolic data that are independent from the anatomical MR information. These tracers help in the definition of glioma extension, detection of anaplastic areas, and postoperative follow-up. Additionally, PET data have a prognostic value independently of histology. To take advantage of PET data in glioma treatment, PET might be integrated in the planning of image-guided biopsy, resection, and radiosurgery.