FDOPA-PET/MRI for Recurrent Pediatric Brain Tumors: Initial Results

Objectives Our primary objective was to assess the feasibility of using the amino acid [F-18]FDOPA in combination with simultaneous PET/MRI to visualize recurrent brain tumors in pediatric patients. Radiolabeled amino acids targeting system L amino acid transport including [C-11]methionine, [F-18]FET, and [F-18]FDOPA are well-established for adult neuro-oncology, but there are relatively few studies reported in pediatric populations.

Methods Pediatric patients with recurrent brain tumors with planned treatment with the anti-VEGF antibody bevacizumab were enrolled. FDOPA-PET and MRI data were acquired simultaneously using a Siemens mMR system. Baseline dynamic FDOPA-PET/MRI was performed immediately prior to starting therapy, and repeat FDOPA-PET/MRI was performed at 4 weeks after initiation of bevacizumab therapy. The FDOPA-PET images were evaluated using maximum and mean standardized uptake values (SUVs) and metabolic tumor volumes (MTVs).

Results 5 patients ranging from 8 to 12 years of age with recurrent brain tumors underwent baseline imaging. Histologies included pilocytic astrocytoma and small cell glioma. FDOPA-PET/MRI was well-tolerated without adverse events. After initial flow, the peak tumor uptake of FDOPA typically occurred at approximately 10 min after injection. All recurrent tumors (n=6) were well-visualized with FDOPA on the baseline images with tumor to brain ratios ranging from 1.5 to 2.7 at 10 to 15 min after injection. At 10 to 15 min after injection, maximum SUVs in the tumor ranged from 2.0 to 4.1 and mean SUVs from 1.3 to 2.3. Changes in MTVs after therapy ranged from 33% to 61% using a cut-off of 1.5 fold above normal frontal lobe (n=3).

Conclusions FDOPA-PET/MRI is feasible for imaging pediatric brain tumors. Our initial results suggest that the performance of FDOPA in this population is similar to adults. Evaluation of early changes in MTVs measured with FDOPA to predict response to bevacizumab is ongoing.

Research Support This research was supported by American Cancer Society, the Mallinckrodt Institute of Radiology, NIH/NCI grant K08CA154790 and the Washington University Institute of Clinical and Translational Sciences which is, in part, supported by the NIH/NCATS CTSA grant UL1TR000448.