**7. Somatostatin-based probes**

Meningiomas are the most common non-glial primary tumors of the central nervous system accounting for approximately 15% of all intracranial tumors (Buetow et al. 1991). More than 90% of intracranial meningiomas are slow growing and histopathologically benign but malignant meningiomas are not rare (Buetow et al. 1991; Goldsmith et al. 1994). [18F]FDG uptake in tumor lesions is dependent on glycolytic rate and disruption of blood brain barrier (Roelcke et al. 1995). High expression of the somatostatin receptor (SSTR) subtype 2 (Dutour et al. 1998) in meningiomas offer the possibility of receptor-targeted imaging (Henze et al. 2005; Henze et al. 2001) of meningiomas. In the case of meningiomas with low glycolytic rate and intact BBB (Roelcke et al. 1995), somatostatin receptor based tracers might be more useful for tumor detection and disease management than [18F]FDG. In a clinical study, a somatostatin receptor analog, 68Ga-DOTA-D-Phe1-Tyr3-octreotide (DOTA-TOC) labeled with the positron emitter 68Ga (half-life, 68 min) was evaluated for imaging meningioma (Henze et al. 2001). In contrast to [18F]FDG, this ligand showed higher T/N uptake ratios. The initial results are encouraging but more clinical studies are needed to fully assess the potential of somatostatin receptor based tracers for imaging meningiomas.
