Simultaneous (68)Ga-DOTATOC-PET/MRI for IMRT treatment planning for meningioma: first experience

Abstract

PURPOSE: To evaluate intensity-modulated radiotherapy (IMRT) treatment planning based on simultaneous positron-emission tomography and magnetic resonance imaging (PET/MRI) of meningioma. METHODS AND MATERIALS: A meningioma patient was examined prior to radiotherapy with dedicated planning computed tomography (CT), MRI, PET/CT with gallium-68-labeled DOTATOC ((68)Ga-DOTATOC), and simultaneous (68)Ga-DOTATOC-PET/MRI. The first gross target volume (GTV) was defined based on a combination of separate MR and (68)Ga-DOTATOC-PET/CT imaging (GTV(PET/CT+MR)). Then, the simultaneous PET/MR images were used to delineate a second GTV (GTV(PET/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 PTV(PET/CT+MR) was applied to the PET/MR-based PTV(PET/MR). RESULTS: Generally, target volumes for IMRT treatment planning did not differ between MRI plus (68)Ga-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 PTV(PET/CT+MR). The evaluation of this plan with respect to the PTV(PET/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. CONCLUSION: This 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.