title: An interindividual comparison of O-(2-[18F]fluoroethyl)-L-tyrosine (FET)- and L-[methyl-11C]methionine (MET)-PET in patients with brain gliomas and metastases.
abstract: OBJECTIVE
  L-[methyl-(11)C]methionine (MET)-positron emission tomography (PET) has a high sensitivity and specificity for imaging of gliomas and metastatic brain tumors. The short half-life of (11)C (20 minutes) limits the use of MET-PET to institutions with onsite cyclotron. O-(2-[(18)F]fluoroethyl)-L-tyrosine (FET) is labeled with (18)F (half-life, 120 minutes) and could be used much more broadly. This study compares the uptake of FET and MET in gliomas and metastases, as well as treatment-induced changes. Furthermore, it evaluates the gross tumor volume (GTV) of gliomas defined on PET and magnetic resonance imaging (MRI).
  
  
  METHODS
  We examined 42 patients with pretreated gliomas (29 patients) or brain metastases (13 patients) prospectively by FET- and MET-PET on the same day. Uptake of FET and MET was quantified by standardized uptake values. Imaging contrast was assessed by calculating lesion-to-gray matter ratios. Tumor extension was quantified by contouring GTV in 17 patients with brain gliomas. Gross tumor volume on PET was compared with GTV on MRI. Sensitivity and specificity of MET- and FET-PET for differentiation of viable tumor from benign changes were evaluated by comparing the PET result with histology or clinical follow-up.
  
  
  RESULTS
  There was a strong linear correlation between standardized uptake values calculated for both tracers in cortex and lesions: r = 0.78 (p = 0.001) and r = 0.84 (p < 0.001), respectively. Image contrast was similar for MET- and FET-PET (lesion-to-gray matter ratios of 2.36 ± 1.01 and 2.33 ± 0.77, respectively). Mean GTV in 17 glioma patients was not significantly different on MET- and FET-PET. Both MET- and FET-PET delineated tumor tissue outside of MRI changes. Both tracers provided differentiated tumor tissue and treatment-related changes with a sensitivity of 91% at a specificity of 100%.
  
  
  CONCLUSIONS
  O-(2-[(18)F]fluoroethyl)-L-tyrosine-PET and MET-PET provide comparable diagnostic information on gliomas and brain metastases. Like MET-PET, FET-PET can be used for differentiation of residual or recurrent tumor from treatment-related changes/pseudoprogression, as well as for delineation of gliomas.
authors.affiliation: Department of Radiation Oncology, Albert Ludwigs Universität Freiburg, Freiburg, Germany. anca.grosu@uniklinikfreiburg.de
authors.forename: Anca-Ligia
authors.initials: AL
authors.lastname: Grosu
authors.forename: Sabrina T
authors.initials: ST
authors.lastname: Astner
authors.forename: Eva
authors.initials: E
authors.lastname: Riedel
authors.forename: Carsten
authors.initials: C
authors.lastname: Nieder
authors.forename: Nicole
authors.initials: N
authors.lastname: Wiedenmann
authors.forename: Felix
authors.initials: F
authors.lastname: Heinemann
authors.forename: Markus
authors.initials: M
authors.lastname: Schwaiger
authors.forename: Michael
authors.initials: M
authors.lastname: Molls
authors.forename: Hans-Jürgen
authors.initials: HJ
authors.lastname: Wester
authors.forename: Wolfgang A
authors.initials: WA
authors.lastname: Weber
mesh_terms: D001921:Brain / Q000000981:diagnostic imaging / Q000378:metabolism; D001932:Brain Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000473:pathology / Q000556:secondary; D005910:Glioma / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000473:pathology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008715:Methionine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D009364:Neoplasm Recurrence, Local / Q000000981:diagnostic imaging / Q000378:metabolism; D018365:Neoplasm, Residual; D049268:Positron-Emission Tomography / Q000379:methods*; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013997:Time Factors; D047368:Tumor Burden; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics
chemical_list: C117289:O-(2-fluoroethyl)tyrosine; D014443:Tyrosine; D008715:Methionine; C038344:methionine methyl ester