Between May 2006 and November 2010, a group of 50 consecutive patients with 56 SB meningiomas underwent planning CT, MRI, and 68Ga-DOTATOC-PET/CT (with contrast-enhanced CT) prior to the start of therapy. Fifty meningiomas showed areas with high 68Ga-DOTATOC uptake. Infracranial extension was visible in MRI/CT or PET in 16/50 patients, who formed the study group and were further analysed in a retrospective manner. There was infracranial extension in all patients. In addition, some patients showed extracranial extension to other sites (not infracranial, four orbit and one maxillary sinus). These extensions were not evaluated in this study. The study group included 11 women and 5 men with a mean age of 54.4 (range 25-73) years. Eleven patients had undergone surgery and/or radiotherapy and 5 patients had not received any therapy before. Pathohistologically, there were 7 meningiomas with a WHO grade 1 tumour (9 unknown). Nine meningiomas underwent FSRT as primary treatment without histological confirmation, when imaging morphology and clinical course suggested the diagnosis of a WHO grade I or II meningioma. The study was based on the Declaration of Helsinki and the principles of 'good clinical practice'. The protocol was approved by the ethics committee of our institution. Written informed consent was obtained from all patients before enrolment into the study. Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.
Details of imaging the tumour volume for fractionated radiotherapy in the Charité medical school have been described elsewhere . Briefly, following the planning-CT, MR imaging of the skull was performed with the use of a head coil in most patients with a 1.0 T scanner (Siemens Harmony™, Siemens Medical Solutions, Erlangen, Germany). Regularly, magnetization-prepared rapid gradient echo (MP-RAGE) T1-weighted sequences were used for coregistration after intravenous application of Gadolinium-DTPA ([Gd], Magnevist™, Schering AG, Berlin, Germany) at a dosage of 0.1 mmol/kg of body weight. These 3-D volume datasets at a 1- (to 1.5) mm slice thickness offer high spatial resolution and allow for coronal and sagittal reformations, enabling contouring in orthogonal planes.
Details of functional imaging have been described previously . 68Ga-DOTATOC was applied intravenously followed by a tracer uptake phase of 60 min, as recommended by Henze et al. . The applied dose of 68Ga-DOTATOC was between 70 and 120 MBq (1.9-3.2 mCi). The patient was placed in a dedicated positioning device for the head using an additional cushion and bandages for fixation. A contrast enhanced low-dose CT scan (detector collimation, 16 × 1.5 mm; tube current, 100 mAs; tube voltage, 120 kV; gantry rotation time, 0.8 s) of the entire head was performed for attenuation correction. PET was acquired in a single bed position with a 16 cm axial FOV from the base of the skull to the vertex and an emission time of 20 minutes. PET emission data were reconstructed as coronal, axial, and sagittal using a 128 × 128 matrix.
Planning-CT, MRI, and PET data were coregistered using the treatment planning software BrainSCAN™ v.5.1 (BrainLAB AG, Feldkirchen, Germany). CT, MRI, and PET were fused automatically using image fusion software and a mutual information algorithm. The validity of image fusion has been successfully tested previously by Grosu et al. .
The windowing of 68Ga-DOTATOC-PET was defined visually following the method published by Astner et al. . The threshold of PET was adapted to tumours visible by MRI in regions where the tumour bordered normal brain tissue and could be outlined with high precision, e.g., where the meningioma bordered normal brain matter. Under the assumption that the 68Ga-DOTATOC-PET uptake in meningiomas is homogeneous , the tumour borders (defined on 68Ga-DOTATOC-PET images in slices with well defined borders by MRI) were used to outline the tumour margins on 68Ga DOTATOC-PET images in regions where the margins were not visible by MRI.
All examinations in one patient were performed within a time frame of 14 days. A checklist for local tumour extension and infiltration of bone and sites was used in this study. Conventional imaging findings were regularly interpreted by two experienced radiologists. Using a dedicated workstation, two experienced nuclear medicine physicians interpreted PET/CT fused images and their CT and PET components. If there was disagreement, the comparison results were reached by consensus.
The planning CT scans obtained with bone window settings (window width 2000 Hounsfield units, centre level 500 Hounsfield units) were used to determine the signs of erosion of adjacent bone or hyperostotic changes . Tumour-specific abnormalities were defined as hyperintense or Gd enhancing structures in MRI and tracer enhancing areas in PET, often a "side-to-side" comparison with MRI was used to determine if a structure was normal or abnormal . Visualization of bony structure changes, tumours spreading to the bony canals or foramina, communication with the middle fossa, and infracranial tumour expansion were compared in MRI, CT, and PET images. In an additional step, the infracranial volume was delineated using MRI/CT and 68Ga DOTATOC-PET separately. The statistical software R, version 2.11.1 (R Foundation for Statistical Computing, Vienna, Austria) was used for statistical analysis. Non-parametric differences were analysed using the Wilcoxon test (at a 0.05 level of significance).