Study on intracranial meningioma using PET ligand investigation during follow-up over years (SIMPLIFY).

PURPOSE Radiologic follow-up of patients with a meningioma at the skull base or near the venous sinuses with magnetic resonance imaging (MRI) after stereotactic radiotherapy (SRT) and neurosurgical resection(s) can be difficult to interpret. This study evaluates the addition of 11C-methionine positron emission tomography (MET-PET) to the regular MRI follow-up. METHODS This prospective pilot study included patients with predominantly WHO grade I meningiomas at the skull base or near large vascular structures. Previous SRT was part of their oncological treatment. A MET-PET in adjunct to their regular MRI follow-up was performed. The standardized uptake value (SUV) was determined for the tumor and the healthy brain, on the pre-SRT target delineation MET-PET and the follow-up MET-PET. Tumor-to-normal ratios were calculated, and 11C-methionine uptake over time was analyzed. Agreement between the combined MRI/MET-PET report and the MRI-only report was determined using Cohen's κ. RESULTS Twenty patients with stable disease underwent an additional MET-PET, with a median follow-up of 84 months after SRT. Post-SRT SUV T/N ratios ranged between 2.16 and 3.17. When comparing the pre-SRT and the post-SRT MET-PET, five categories of SUV T/N ratios did not change significantly. Only the SUVpeak T/Ncortex decreased significantly from 2.57 (SD 1.02) to 2.20 (SD 0.87) [p = 0.004]. A κ of 0.77 was found, when comparing the MRI/MET-PET report to the MRI-only report, indicating no major change in interpretation of follow-up data. CONCLUSION In this pilot study, 11C-methionine uptake remained remarkably high in meningiomas with long-term follow-up after SRT. Adding MET-PET to the regular MRI follow-up had no impact on the interpretation of follow-up imaging.