title: Semiquantitative analysis of C-11 methionine PET may distinguish brain tumor recurrence from radiation necrosis even in small lesions.
abstract: OBJECTIVE
  (11)C-Methionine positron emission tomography (MET-PET) has been used to distinguish brain tumor recurrence from radiation necrosis. Because the spatial resolution of conventional PET scanners is low, partial volume effect (PVE) may decrease the detectability of small tumor recurrence. The aim of this study is to investigate the diagnostic value of MET-PET upon semiquantitative analyses in particular PVE-affected small lesions.
  
  
  METHODS
  First, we performed a phantom experiment to investigate what size lesion is affected by PVE. This study included 29 patients (33 lesions) suspected of recurrent brain tumors by magnetic resonance imaging (MRI) after radiation therapy. All of them received MET-PET. Semiquantitative analysis was performed using maximum standardized uptake value (SUVmax) and lesion-versus-normal ratio (L/N ratio). ROC analysis was also assessed about the diagnostic value of MET-PET.
  
  
  RESULTS
  From the result of the phantom experiment, lesions smaller than 20 mm in brain mode or smaller than 30 mm in whole-body mode were defined as PVE-affected lesions. Histological analysis or clinical follow-up confirmed the diagnosis of tumor recurrence in 22 lesions, and radiation necrosis in 11 lesions. L/N ratios of recurrence and necrosis for overall lesions were 1.98 ± 0.62 and 1.27 ± 0.28, respectively (p < 0.01). In the PVE-affected lesions, L/N ratio for recurrence (1.72 ± 0.44) was also significantly higher than that for necrosis (1.20 ± 0.11) (p < 0.01). On the ROC analysis for the PVE-affected lesions, the area under the curve for L/N ratio (0.897) was significantly higher than that for SUVmax (0.718) (p < 0.05). These areas under the curve were almost equal to that of overall lesions for L/N ratio (0.886) and for SUVmax (0.738).
  
  
  CONCLUSIONS
  Semiquantitative analysis of MET provided high diagnostic value even for PVE-affected small lesions. MET-PET enables early diagnosis of recurrence of brain tumor in the follow-up after the radiation therapy.
authors.affiliation: Department of Nuclear Medicine, Hokkaido University Graduate School of Medicine, North 15th, West 7th, Kitaku, Sapporo, 060-8638, Japan. shozo@med.hokudai.ac.jp
authors.forename: Shozo
authors.initials: S
authors.lastname: Okamoto
authors.forename: Tohru
authors.initials: T
authors.lastname: Shiga
authors.forename: Naoya
authors.initials: N
authors.lastname: Hattori
authors.forename: Naoki
authors.initials: N
authors.lastname: Kubo
authors.forename: Toshiki
authors.initials: T
authors.lastname: Takei
authors.forename: Norio
authors.initials: N
authors.lastname: Katoh
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Sawamura
authors.forename: Kenichi
authors.initials: K
authors.lastname: Nishijima
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kuge
authors.forename: Nagara
authors.initials: N
authors.lastname: Tamaki
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001921:Brain / Q000000981:diagnostic imaging* / Q000473:pathology*; D001932:Brain Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008297:Male; D008715:Methionine; D008875:Middle Aged; D009336:Necrosis; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography; D011832:Radiation Injuries / Q000000981:diagnostic imaging* / Q000473:pathology*; D012008:Recurrence; D012189:Retrospective Studies; D047368:Tumor Burden; D055815:Young Adult
chemical_list: C086242:carbon-11 methionine; D008715:Methionine