The Application of Magnetic Resonance Imaging-Deformed 11C-Methionine-Positron Emission Tomography Images in Stereotactic Radiosurgery

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Abstract
Background: Although 11C-methionine positron emission tomography (MET-PET) images can be fused with magnetic resonance (MR) images using planning software for gamma knife radiosurgery (GKR), the stereotactic information has limited value in patients with recurrent malignant brain tumor due to the difference in imaging protocols between MET-PET and MR images. The aim of this study was to evaluate the clinical application of MR imaging (MRI)-deformed MET-PET images in GKR using a deformable registration tool. Methods: We examined the enhanced MR stereotactic images, MET-PET and MRI-deformed MET-PET images without stereotactic information for 12 newly developed metastatic brain tumors. MET-PET and MRI-deformed MET-PET images were co-registered with the MR stereotactic images using radiosurgery planning software. Visual analysis was performed to determine whether the MET-PET and MR images matched better after using the deformable registration tool. In addition, the matching volume between MR and MET-PET images was compared before and after applying this tool. The matching volume was calculated as the metabolic tumor volume on the MET-PET images, including the MR-enhanced volume. The matching percentage was calculated as the matching volume divided by the MR-enhanced volume, multiplied by 100. Results: Visual analysis revealed that the MRI-deformed MET-PET images provided the same axial plane as that of the MR images, with the same window level, enabling easy identification of the tumor with the radiosurgery planning software. The mean matching percentage of the MET-PET/MR fusion images was 61.1% (range 24.7–94.7) and that of the MRI-deformed MET-PET/MR fusion images was 63.4% (range 20.8–94.3). No significant difference was found in the matching percentage between the two types of fusion images (p = 0.754). Conclusions: The MRI-deformed MET-PET images enable utilization of the functional information when planning a treatment in GKR without significant volume change.

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