Comparison of ¹¹C-Methionine and ¹⁸F-FDG PET/CT for Staging and Follow-up of Pediatric Lymphoma.

Abstract

Methionine transport across plasma membranes occurs via the large amino acid transporter, which is overexpressed in malignant cells, leading to tracer accumulation within tumors. We investigated the uptake of ¹¹C-methionine (¹¹C-MET) in children and young adults with Hodgkin lymphoma (HL) or non-Hodgkin lymphoma (NHL) and compared the biodistribution of ¹¹C-MET PET/CT with that of ¹⁸F-FDG PET/CT. <b>Methods:</b> Conducted under an investigational new drug authorization, we prospectively enrolled patients with newly diagnosed HL (<i>n</i> = 19) and NHL (<i>n</i> = 2) onto the Institutional Review Board-approved investigation of ¹¹C-MET PET/CT. After a minimum 4-h fast, patients received 740 MBq/1.7 m² (maximum, 740 MBq [20 mCi/1.7 m²; maximum, 20 mCi]) of ¹¹C-methionine intravenously. PET/CT was performed 5 min after injection from the vertex to thighs at 3 min per bed position. In a separate session, patients received 5.5 MBq/kg (maximum, 485 MBq [0.15 mCi/kg; maximum, 12 mCi]) of ¹⁸F-FDG with imaging initiated approximately 1 h after radiopharmaceutical administration. All studies were reviewed by consensus of 2 senior imaging specialists. The presence of metabolic activity on baseline studies was compared among 17 nodal groups. <b>Results:</b> Eighteen patients (11 male; median age, 15.2 y; age range, 9.5-22.6 y) comprised the study cohort. All had paired ¹¹C-MET PET/CT and ¹⁸F-FDG PET/CT studies at diagnosis. At baseline, 3 nodal groups demonstrating discordant metabolic activity by both ¹⁸F-FDG PET/CT and ¹¹C-MET PET/CT were Waldeyer's ring, paraaortic region, and the liver. All others were found to have concordant metabolic activity. Normal intense ¹¹C-MET uptake in the pancreas and liver reduced sensitivity for disease detection in these regions. At follow-up, 14 of 15 study pairs had concordant results. <b>Conclusion:</b>¹¹C-MET uptake is elevated in most regions involved with lymphoma at diagnosis and follow-up. Its utility in the abdomen is limited by uptake in normal structures.