Imaging Brain Metastasis Patients With 18F-(2S,4R)-4-Fluoroglutamine

There is a need for an alternative PET probe, which does not show normal brain tissue uptake in the evaluation of metastasis to the brain. Therefore, we investigate the feasibility of F-labeled glutamine analog, F-(2S,4R)-4-fluoroglutamine (F-FGln), as a new metabolic probe to detect brain metastasis.

Patients (7 men and 7 women; age, 25-67 years) with suspected brain metastasis were enrolled for this study. All patients were imaged first with F-FGln PET (3 patients for 1-hour dynamic whole-body PET/CT scans, and 11 patients for static whole-body scans at 30 ± 10 minutes after injection), followed by a whole-body F-FDG PET performed in the same week. The characteristics of F-FGln PET imaging in brain metastasis patients were compared with that of F-FDG PET and/or contrast-enhanced MRI patient-by-patient. A composite of all functional and anatomic imaging studies served as the imaging comparator.

Initial study in 3 patients using 1-hour dynamic scan showed that 30 ± 10 minutes after injection is optimal for identifying brain metastasis with a high-contrast ratio. All patients were positive for brain metastasis on this studies that demonstrated 38 lesions in 6 anatomic regions on the imaging comparator. The per-lesion detection rates for F-FGln PET and F-FDG PET were 81.6% and 36.8%, respectively. The average tumor-to-normal brain ratio of F-FGln PET was significantly better than that of F-FDG PET in all patients (4.97 ± 2.23 vs 1.22 ± 0.69, P < 0.05). Furthermore, our results suggest that F-FGln uptake in brain metastasis appeared to be independent of tumor size and peripheral edema. In addition, in 14 brain metastatic lesions visualized by both F-FDG PET and F-FGln PET imaging, a positive correlation of SUVmax was observed (r = 0.780, P < 0.01). As to the extracranial metastasis, both tracers showed a concordant increased radioactive uptake except in liver and bone.

The initial imaging of F-FGln presenting a promising new PET radiotracer for patients with brain metastasis and its utility in the liver and bone metastatic lesions may require more caution due to uptake in normal structures.