11C-Methionine uptake in meningiomas after stereotactic radiotherapy

Objective 11 C-Methionine positron emission tomography (MET-PET) is used for stereotactic radiotherapy planning in meningioma patients. The role of MET-PET during subsequent follow-up (FU) is unclear. We analyzed the uptake of 11 C-Methionine before and after stereotactic radiotherapy (SRT) in patients with a complex meningioma and investigated if there was a difference between patients with progressive disease (PD) and stable disease (SD) during FU. Methods This retrospective study investigates 62 MET-PETs in 29 complex meningioma patients. Standardized uptake value (SUV) max and SUV peak tumor-to-normal ratios (T/N-ratios) were calculated, comparing the tumor region with both the mirroring intracranial area and the right frontal gray matter. The difference in 11 C-Methionine uptake pre- and post-SRT was analyzed, as well as the change in uptake between PD or SD. Results Median (IQR) FU duration was 67 months (50.5–91.0). The uptake of 11 C-Methionine in meningiomas remained increased after SRT. Neither a statistically significant difference between MET-PETs before and after SRT was encountered, nor a significant difference in one of the four T/N-ratios between patients with SD versus PD with median (IQR) SUV max T/N R front 2.65 (2.13–3.68) vs 2.97 (1.55–3.54) [ p = 0.66]; SUV max T/N mirror 2.92 (2.19–3.71) vs 2.95 (1.74–3.60) [ p = 0.61]; SUV peak T/N R front 2.35 (1.64–3.40) vs 2.25 (1.44–3.74) [ p = 0.80]; SUV peak T/N mirror 2.38 (1.91–3.36) vs 2.35 (1.56–3.72) [ p = 0.95]. Conclusions Our data do not support use of MET-PET during FU of complex intracranial meningiomas after SRT. MET-PET could not differentiate between progressive or stable disease.