PET imaging of somatostatin receptors using [(68)GA]DOTA-D-Phe(1)-Tyr(3)-octreotide: First results in patients with meningiomas

Imaging of somatostatin receptors (SSTRs) using [In-111]diethylenetriaminep entaacetic-acid-octreotide (DTPAOC) has proven to be helpful in the differe ntiation of meningiomas, neurinomas or neurofibromas, and metastases as wel l as in the follow-up of meningiomas, A drawback of the SPECT method is its limited sensitivity in detecting small meningiomas. Because of PET's incre ased spatial resolution and its ability to absolutely quantify biodistribut ion, a PET tracer for SSTR imaging would be desirable. Methods: 1,4,7,10-te traazacyclododecane-N,N ' ,N "N ' ' ' -tetraacetic-acid-D-Phe(1)-Tyr(3)-oct reotide (DOTATOC) was labeled using the positron-emitting generator nuclide Ga-68. We acquired dynamic PET images over 120 min after intravenous injec tion of 175 MBq [Ga-68]DOTATOC in 3 patients suffering from 8 meningiomas ( WHO I-o; 7- to 25-mm diameter). Patients' heads had been fixed using indivi dually shaped fiber masks equipped with an external stereotactic localizer system to match PET, CT, and MRI datasets. Results: [68Ga]DOTATOC was rapid ly cleared from the blood (half-life alpha, 3.5 min; half-life beta, 63 min ). Standardized uptake values (SUVs) of meningiomas increased immediately a fter injection and reached a plateau 60-120 min after injection (mean SUV, 10.6). No tracer could be found in the surrounding healthy brain tissue. AH meningiomas (even the 3 smallest [7- to 8-mm diameter]) showed high tracer uptake and could be visualized clearly. Tracer boundaries showed a good co rrespondence with the matched CT and MRI images. PET provided valuable addi tional information regarding the extent of meningiomas located beneath osse ous structures, especially at the base of the skull. Conclusion: According to our initial experiences, [Ga-68]DOTATOC seems to be a very promising new PET tracer for imaging SSTRs even in small meningiomas, offering excellent imaging properties and a very high tumor-to-background ratio.