• Daniela Thorwarth, Guido Henke, Arndt-Christian Müller, Matthias Reimold, Thomas Beyer, Andreas Boss, Armin Kolb, Bernd Pichler, and Christina Pfannenberg.
• Section of Biomedical Physics, University Hospital for Radiation Oncology, Eberhard-Karls-Universität Tübingen, Tübingen, Germany. daniela.thorwarth@med.uni-tuebingen.de
• Int. J. Radiat. Oncol. Biol. Phys. 2011 Sep 1; 81 (1): 277-83.

PurposeTo evaluate intensity-modulated radiotherapy (IMRT) treatment planning based on simultaneous positron-emission tomography and magnetic resonance imaging (PET/MRI) of meningioma.Methods And MaterialsA meningioma patient was examined prior to radiotherapy with dedicated planning computed tomography (CT), MRI, PET/CT with gallium-68-labeled DOTATOC (68Ga-DOTATOC), and simultaneous 68Ga-DOTATOC-PET/MRI. The first gross target volume (GTV) was defined based on a combination of separate MR and 68Ga-DOTATOC-PET/CT imaging (GTVPET/CT+MR). Then, the simultaneous PET/MR images were used to delineate a second GTV (GTVPET/MR) by following exactly the same delineation strategy. After an isotropic expansion of those volumes by a 4-mm safety margin, the resulting planning target volumes (PTVs) were compared by calculating the intersection volume and the relative complements. A cross-evaluation of IMRT plans was performed, where the treatment plan created for the PTVPET/CT+MR was applied to the PET/MR-based PTVPET/MR.ResultsGenerally, target volumes for IMRT treatment planning did not differ between MRI plus 68Ga-DOTATOC-PET/CT and simultaneous PET/MR imaging. Only in certain regions of the GTV were differences observed. The overall volume of the PET/MR-based PTV was approximately the same as that obtained from PET/CT data. A small region of infiltrative tumor growth next to the main tumor mass was better visualized with combined PET/MR due to smaller PET voxel sizes and improved recovery. An IMRT treatment plan was optimized for the PTVPET/CT+MR. The evaluation of this plan with respect to the PTVPET/MR showed parts of the target volume that would not have received the full radiation dose after delineation of the tumor, based on simultaneous PET/MR.ConclusionThis case showed that differences in target volumes delineated on the basis of separate MR and PET/CT and simultaneous PET/MR may be observed that can have significant consequences for an effectively applied radiotherapy treatment plan.Copyright © 2011 Elsevier Inc. All rights reserved.

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