PET imaging of brain tumors

The most commonly used radiopharmaceuticals for positron emission tomography (PET) imaging of brain tumors are (11)C-methionine and (18)F-fluorethyl-tyrosine. These compounds are mainly applied to better define the extension of gliomas during radiation treatment planning and to differentiate recurrent tumors from treatment associated changes. (11)C-methionine and (18)F-fluorethyl-tyrosine demonstrate a very similar accuracy for these applications. In addition to radiolabeled amino acids (68)gallium-labeled somatostatin analogs can be used for imaging of meningiomas. In contrast to extracranial tumors the glucose analogue (18)F-fluorodeoxyglucose (FDG) plays only a limited role in brain tumor imaging, as the high glucose utilization of the normal brain results in poor contrast between gray matter and tumor tissue. Ongoing clinical trials are presently evaluating radiopharmaceuticals for imaging of tumor proliferation and hypoxia. Using these markers it may become feasible to define tumor subvolumes harboring cancer cells with high biological aggressiveness and treat those subvolumes with higher radiation doses by intensity modulated radiotherapy.