Evaluation of 11 C-methionine PET and anatomic MRI associations in diffuse intrinsic pontine glioma.

The role of metabolic imaging in the diagnosis, treatment, and response assessment of diffuse intrinsic pontine glioma (DIPG) is poorly-defined. We investigated the uptake of 11 C-methionine (11 C-MET) in pediatric patients with newly diagnosed DIPG and evaluated the associations of 11 C-MET positron emission tomography (PET) metrics with conventional MRI indices and survival outcomes. Methods: Twenty-two patients with newly diagnosed DIPG were prospectively enrolled on an IRB-approved investigational study of 11 C-MET-PET. All patients underwent baseline 11 C-MET-PET/CT, and initial treatment-response scans after (chemo)radiation were obtained for 17 patients. Typical and atypical DIPGs were assessed clinically and radiographically and defined by multidisciplinary consensus. Three-dimensional regions of interest (ROIs), reviewed by consensus between a nuclear medicine physician and a radiation oncologist, were delineated after co-registration of PET and MR images. Associations of 11 C-MET uptake intensity and uniformity with survival, along with associations between 11 C-MET uptake and conventional MRI tumor indices over time, were evaluated. 11 C-MET-PET voxel values within ROIs were assessed as threshold values across proportions of the study population, and 11 C-MET uptake at baseline was assessed relative to MRI-defined tumor progression. Results: 11 C-MET uptake above that of uninvolved brain tissue was observed in 18/22 baseline scans (82%) and 15/17 initial response scans (88%). 11 C-MET avidity within MRI-defined tumor was limited in extent, with 11/18 positive baseline 11 C-MET-PET scans (61%) showing less than 25% 11 C-MET-avid tumor. The increase in total tumor volume with 11 C-MET-PET was relatively limited (17.2%, IQR 6.53%-38.90%), as was the extent of 11 C-MET uptake beyond the MRI-defined tumor (2.2%, IQR 0.55%-10.88%). Although baseline 11 C-MET-PET intensity and uniformity metrics did not correlate with survival outcomes, initial 11 C-MET avidity overlapped with recurrent tumor in 100% of cases. A clinical diagnosis of atypical DIPG was associated with borderline significantly prolonged progression-free survival (P = 0.07), yet 11 C-MET-PET indices at diagnosis did not differ significantly between atypical and typical DIPGs.