Differentiating radiation necrosis from tumor recurrence in high-grade gliomas: assessing the efficacy of 18F-FDG PET, 11C-methionine PET and perfusion MRI.

Purpose: The authors analyzed the characteristics of perfusion magnetic resonance imaging (MRI), (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET) and (11)C-methionine (MET) PET to compare the efficacies of these modalities in making the distinction between radiation necrosis and tumor recurrence of high-grade glioma.

Patients And Methods: Ten patients were evaluated with dynamic susceptibility contrast perfusion MRI, (11)C-MET PET and (18)F-FDG PET to visualize gadolinium-enhanced lesions during the post-radiation follow-up period. In the perfusion MRI, four regions of interest (ROIs) were identified and average values were calculated. A reference ROI of the same size was defined in the contralateral white matter to obtain the relative cerebral blood volume (rCBV). After coregistering the PET images with the MRI, we measured the maximum uptake values of the lesion and of the contralateral cerebral white matter as reference area to calculate the L(max)/R(max) ratio.

Results: The rCBV was higher in the recurrence group than in the necrosis group (p=0.010). There was no difference between groups in terms of the L(max)/R(max) ratio as derived from the (18)F-FDG and (11)C-MET PET.

Conclusion: A quantitative rCBV as calculated from a perfusion MRI scan might be superior to the L(max)/R(max) ratio as derived from (18)F-FDG and (11)C-MET PET in order to distinguish a recurrence of high-grade glioma from radiation necrosis.