title: Intra-individual comparison of ¹⁸F-FET and ¹⁸F-DOPA in PET imaging of recurrent brain tumors.
abstract: BACKGROUND
  Both (18)F-fluorodihydroxyphenylalanine ((18)F-DOPA) and (18)F-fluoroethyltyrosine ((18)F-FET) have already been used successfully for imaging of brain tumors. The aim of this study was to evaluate differences between these 2 promising tracers to determine the consequences for imaging protocols and the interpretation of findings.
  
  
  METHODS
  Forty minutes of dynamic PET imaging were performed on 2 consecutive days with both (18)F-DOPA and (18)F-FET in patients with recurrent low-grade astrocytoma (n = 8) or high-grade glioblastoma (n = 8). Time-activity-curves (TACs), standardized uptake values (SUVs) and compartment modeling of both tracers were analyzed, respectively.
  
  
  RESULTS
  The TAC of DOPA-PET peaked at 8 minutes p.i. with SUV 5.23 in high-grade gliomas and 10 minutes p.i. with SUV 4.92 in low-grade gliomas. FET-PET peaked at 9 minutes p.i. with SUV 3.17 in high-grade gliomas and 40 minutes p.i. with SUV 3.24 in low-grade gliomas. Neglecting the specific uptake of DOPA into the striatum, the tumor-to-brain and tumor-to-blood ratios were higher for DOPA-PET. Kinetic modeling demonstrated a high flow constant k1 (mL/ccm/min), representing cellular internalization through AS-transporters, for DOPA in both high-grade (k1 = 0.59) and low-grade (k1 = 0.55) tumors, while lower absolute values and a relevant dependency from tumor-grading (high-grade k1 = 0.43; low-grade k1 = 0.33) were observed with FET.
  
  
  CONCLUSIONS
  DOPA-PET demonstrates superior contrast ratios for lesions outside the striatum, but SUVs do not correlate with grading. FET-PET can provide additional information on tumor grading and benefits from lower striatal uptake but presents lower contrast ratios and requires prolonged imaging if histology is not available in advance due to a more variable time-to-peak.
authors.affiliation: Department of Nuclear Medicine, University Hospital of Heidelberg, Heidelberg, Germany (C.K., K.L., A.A-O., U.H., F.L.G.); Department of Radiation Oncology, University Hospital of Heidelberg, Heidelberg, Germany (S.E.C., S.R., J.D.).
authors.forename: Clemens
authors.initials: C
authors.lastname: Kratochwil
authors.forename: Stephanie E
authors.initials: SE
authors.lastname: Combs
authors.forename: Karin
authors.initials: K
authors.lastname: Leotta
authors.forename: Ali
authors.initials: A
authors.lastname: Afshar-Oromieh
authors.forename: Stefan
authors.initials: S
authors.lastname: Rieken
authors.forename: Jürgen
authors.initials: J
authors.lastname: Debus
authors.forename: Uwe
authors.initials: U
authors.lastname: Haberkorn
authors.forename: Frederik L
authors.initials: FL
authors.lastname: Giesel
mesh_terms: D001254:Astrocytoma / Q000000981:diagnostic imaging*; D001932:Brain Neoplasms / Q000000981:diagnostic imaging*; D004295:Dihydroxyphenylalanine / Q000031:analogs & derivatives*; D005909:Glioblastoma / Q000000981:diagnostic imaging*; D006801:Humans; D009364:Neoplasm Recurrence, Local / Q000000981:diagnostic imaging*; D049268:Positron-Emission Tomography; D014443:Tyrosine / Q000031:analogs & derivatives*
chemical_list: C545932:(18F)fluoroethyltyrosine; C043437:fluorodopa F 18; D014443:Tyrosine; D004295:Dihydroxyphenylalanine
keywords: DOPA; FET; brain tumor; positron emission tomography