[11C]Methionine PET metabolic imaging of low grade CNS tumors in children and young adults.

Objectives PET imaging of brain tumors with amino acid-based radiotracers provides the advantage of a low background activity in the cortex and white matter not affected by the disease. In the current study, we examined the ability of PET with [11C]methionine (METPET) to visualize low grade CNS tumors in children and young adults.

Methods The study included 41 patients with age range from 4 to 27 years (17 male, 24 female). 18 patients had METPET performed at the primary diagnosis. 23 patients underwent study at the time of known or suspected recurrence. After a 4 hour or longer fast, patients were injected intravenously with 20 mCi (740MBq) [11C]methionine/1.7 sq m body surface area (prepared under IND specified conditions). Approximately 5 minutes later, CT of the head was obtained for attenuation correction, followed by emission imaging for 15 min in 3D mode. Images were reconstructed using vendor supplied software. Two experienced nuclear medicine physicians reviewed images using quantitative (SUVmax) and qualitative approaches with comparison to MRI.

Results At diagnosis, 12 of 18 patients had uptake within the tumor at least 2 times greater than the white matter background. In the initial scans of the patients with known or suspected recurrent disease, tumor uptake was greater than the background in 19 out of 23 patients. Table 1 depicts the tumor to background ratios for patients at initial diagnosis and for those with recurrent disease. Tumor uptake tended to be slightly higher in previously treated patients. In four patients, methionine uptake did not differ significantly from the background. In 2 patients a contemporary [18F]FDG PET was also performed. In both cases, METPET provided significant improvement in tumor visualization and tumor/background ratio (Picture 1).

Conclusions : In most patients with low grade CNS tumors, PET with [11C]methionine provides a high quality functional imaging tool for metabolic characterization. Uptake was elevated in both newly diagnosed patients and in those with recurrent disease. The low background activity in both cerebral gray and white matter facilitates tumor detection. Serial studies will determine the utility of the technique in assessing prognosis, response to therapy, monitoring for tumor recurrence, and distinguishing recurrent tumor from radiation necrosis. $$graphic_613DC5E1-56AD-4064-8973-23939E4A339B$$