• Stefanie Milker-Zabel, Angelika Zabel-du Bois, Marcus Henze, Peter Huber, Daniela Schulz-Ertner, Angelika Hoess, Uwe Haberkorn, and Jürgen Debus.
• Department of Radiation Oncology, Radiation Therapy, University of Heidelberg, Heidelberg, Germany. stefanie_milker-zabel@med.uni-heidelberg.de
• Int. J. Radiat. Oncol. Biol. Phys. 2006 May 1; 65 (1): 222-7.

PurposeTo evaluate the influence of 68-Ga-labeled DOTA (0)-D-Phe (1)-Tyr (3)-Octreotide positron emission tomography ([68Ga]-DOTATOC-PET) for target definition for fractionated stereotactic radiotherapy (FSRT) as a complementary modality to computed tomography (CT) and magnetic resonance imaging (MRI). Because meningiomas show a high expression of somatostatin receptor subtype 2, somatostatin analogs such as DOTATOC offer the possibility of receptor-targeted imaging.Patients And MethodsTwenty-six patients received stereotactic CT, MRI, and [68Ga]-DOTATOC-PET as part of their treatment planning. Histology was: World Health Organization (WHO) Grade 1 61.5%, WHO Grade 2 7.7%, WHO Grade 3 3.9%, and undetermined 26.9%. Six patients received radiotherapy as primary treatment, 2 after subtotal resection; 17 patients were treated for recurrent disease. Dynamic PET scans were acquired before radiotherapy over 60 min after intravenous injection of 156 +/- 29 MBq [68Ga]-DOTATOC. These PET images were imported in the planning software for FSRT. Planning target volume (PTV)-I outlined on CT and contrast-enhanced MRI was compared with PTV-II outlined on PET. PTV-III was defined with CT, MRI, and PET and was actually used for radiotherapy treatment.ResultsPTV-III was smaller than PTV-I in 9 patients, the same size in 7 patients, and larger in 10 patients. Median PTV-I was 49.6 cc, median PTV-III was 57.2 cc. In all patients [68Ga]-DOTATOC-PET delivered additional information concerning tumor extension. PTV-III was significantly modified based on DOTATOC-PET data in 19 patients. In 1 patient no tumor was exactly identified on CT/MRI but was visible on PET.ConclusionThese data demonstrate that [68Ga]-DOTATOC-PET improves target definition for FSRT in patients with intracranial meningiomas. Radiation targeting with fused DOTATOC-PET, CT, and MRI resulted in significant alterations in target definition in 73%.

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