18 F-FDOPA PET/CT Combined with MRI for Gross Tumor Volume Delineation in Patients with Skull Base Paraganglioma.

In this simulation study, we assessed differences in gross tumor volume (GTV) in a series of skull base paragangliomas (SBPGLs) using magnetic resonance imaging (MRI), F-18-dihydroxyphenylalanine (F-18-FDOPA) combined positron emission tomography/computed tomography (PET/CT), and F-18-FDOPA PET/MRI images obtained by rigid alignment of PET and MRI. GTV was delineated in 16 patients with SBPGLs on MRI (GTV(MRI)), F-18-FDOPA PET/CT (GTV(PET)), and combined PET/MRI (GTV(PET/MRI)). GTV(PET/MRI) was the union of GTV(MRI) and GTV(PET) after visual adjustment. Three observers delineated GTV(MRI) and GTV(PET/MRI) independently. Excellent interobserver reproducibility was found for both GTV(MRI) and GTV(PET/MRI). GTV(PET) and GTV(MRI) were not significantly different. However, there was some spatial difference between the locations of GTV(MRI), GTV(PET), and GTV(PET/MRI). The Dice similarity coefficient median value was 0.4 between PET/CT and MRI, and 0.8 between MRI and PET/MRI. The combined use of PET/MRI produced a larger GTV than MRI alone. Nevertheless, both the target-delivered dose and organs-at-risk conservancy were respected when treatment was planned on the PET/MRI-matched data set. Future integration of F-18-FDOPA PET/CT into clinical practice will be necessary to evaluate the influence of this diagnostic modality on SBPGL therapeutic management. If the clinical utility of F-18-FDOPA PET/CT and/or PET/MRI is confirmed, GTV(PET/MRI) should be considered for tailored radiotherapy planning in patients with SBPGL.