Improved Target Volume Definition in Patients with Intracranial Meningiomas by Correlation of CT, MRI and [68Ga]-DOTATOC PET for Fractionated Stereotactic Radiotherapy

Abstract

Purpose/Objective: To evaluate the influence and accuracy of [68Ga]-DOTATOC PET for target volume definition in patients with intracranial meningiomas as a complimentary modality to CT and MRI. Meningiomas show high expression of the somatostatin-receptor subtype 2. Therefore, the somatostatin analogue DOTATOC which is labeled with the positron emitting generator radionuclide 68Ga (t½ =68min) is used for the visualization of these tumors for stereotactic treatment planning. In contrast to FDG, [68Ga]-DOTATOC shows very high meningioma to background ratios.Materials/Methods: Twenty-six patients with intracranial meningiomas received stereotactic CT, MRI and 68Ga-DOTATOC PET as part of their image acquisition for fractionated stereotactic radiotherapy (FSRT) treatment planning. In two patients MRI was not feasible due to pace maker. Tumor distribution was: World Health Organization (WHO) grade I 61.5%, WHO grade II 7.7%, WHO grade III 3.9 and without biopsy 26.9%. Dynamic PET-scans (ECAT EXACT HR+; 3D-Mode; 28 frames; OSEM reconstruction) were acquired before radiotherapy over 60 min after i.v. injection of 156± 29 MBq [68Ga]-DOTATOC. These PET images were imported in the planning software for FSRT dosimetry. The planning target volume I (PTV-I) outlined on CT and T1-MRI contrast enhanced was compared with the planning target volume II (PTV-II) defined with the additional information of DOTATOC PET. For radiotherapy the planning target volume was defined using the combined information of CT, MRI and PET.Results: PTV-II was smaller, the same size, or larger than PTV-I in 9 (35%), 7 (26%), and 10 (39%) patients respectively. Median PTV-II for FSRT was 57.2cc (range, 0.5–432cc), median PTV-I was 49.6cc (range, 2.2–240cc). In all patients [68Ga]-DOTATOC PET delivered additional information concerning tumor extension. The PTV for radiation therapy was significant modified based on DOTATOC PET data in 19 patients. In 1 patient with optic nerve sheath meningioma no tumor was identified on CT and MRI but visible on PET. Six patients received radiotherapy as primary treatment, 2 following subtotal resection, 17 patients were treated for recurrent disease.Conclusions: These data demonstrate that [68Ga]-DOTATOC PET improves target volume definition for fractionated stereotactic radiation therapy in patients with intracranial meningiomas. Radiation targeting with fused DOTATOC PET, CT and MRI resulted in alterations in target volume definition in 19 patients (73%). A differentiation between tumor and pituitary gland in lesions next to the cavernous sinus is not possible. Purpose/Objective: To evaluate the influence and accuracy of [68Ga]-DOTATOC PET for target volume definition in patients with intracranial meningiomas as a complimentary modality to CT and MRI. Meningiomas show high expression of the somatostatin-receptor subtype 2. Therefore, the somatostatin analogue DOTATOC which is labeled with the positron emitting generator radionuclide 68Ga (t½ =68min) is used for the visualization of these tumors for stereotactic treatment planning. In contrast to FDG, [68Ga]-DOTATOC shows very high meningioma to background ratios. Materials/Methods: Twenty-six patients with intracranial meningiomas received stereotactic CT, MRI and 68Ga-DOTATOC PET as part of their image acquisition for fractionated stereotactic radiotherapy (FSRT) treatment planning. In two patients MRI was not feasible due to pace maker. Tumor distribution was: World Health Organization (WHO) grade I 61.5%, WHO grade II 7.7%, WHO grade III 3.9 and without biopsy 26.9%. Dynamic PET-scans (ECAT EXACT HR+; 3D-Mode; 28 frames; OSEM reconstruction) were acquired before radiotherapy over 60 min after i.v. injection of 156± 29 MBq [68Ga]-DOTATOC. These PET images were imported in the planning software for FSRT dosimetry. The planning target volume I (PTV-I) outlined on CT and T1-MRI contrast enhanced was compared with the planning target volume II (PTV-II) defined with the additional information of DOTATOC PET. For radiotherapy the planning target volume was defined using the combined information of CT, MRI and PET. Results: PTV-II was smaller, the same size, or larger than PTV-I in 9 (35%), 7 (26%), and 10 (39%) patients respectively. Median PTV-II for FSRT was 57.2cc (range, 0.5–432cc), median PTV-I was 49.6cc (range, 2.2–240cc). In all patients [68Ga]-DOTATOC PET delivered additional information concerning tumor extension. The PTV for radiation therapy was significant modified based on DOTATOC PET data in 19 patients. In 1 patient with optic nerve sheath meningioma no tumor was identified on CT and MRI but visible on PET. Six patients received radiotherapy as primary treatment, 2 following subtotal resection, 17 patients were treated for recurrent disease. Conclusions: These data demonstrate that [68Ga]-DOTATOC PET improves target volume definition for fractionated stereotactic radiation therapy in patients with intracranial meningiomas. Radiation targeting with fused DOTATOC PET, CT and MRI resulted in alterations in target volume definition in 19 patients (73%). A differentiation between tumor and pituitary gland in lesions next to the cavernous sinus is not possible.