title: Quantitative volumetric analysis of gliomas with sequential MRI and ¹¹C-methionine PET assessment: patterns of integration in therapy planning.
abstract: OBJECTIVE
  The aim of the study was to evaluate the volumetric integration patterns of standard MRI and (11)C-methionine positron emission tomography (PET) images in the surgery planning of gliomas and their relationship to the histological grade.
  
  
  METHODS
  We studied 23 patients with suspected or previously treated glioma who underwent preoperative (11)C-methionine PET because MRI was imprecise in defining the surgical target contour. Images were transferred to the treatment planning system, coregistered and fused (BrainLAB). Tumour delineation was performed by (11)C-methionine PET thresholding (vPET) and manual segmentation over MRI (vMRI). A 3-D volumetric study was conducted to evaluate the contribution of each modality to tumour target volume. All cases were surgically treated and histological classification was performed according to WHO grades. Additionally, several biopsy samples were taken according to the results derived either from PET or from MRI and analysed separately.
  
  
  RESULTS
  Fifteen patients had high-grade tumours [ten glioblastoma multiforme (GBM) and five anaplastic), whereas eight patients had low-grade tumours. Biopsies from areas with high (11)C-methionine uptake without correspondence in MRI showed tumour proliferation, including infiltrative zones, distinguishing them from dysplasia and radionecrosis. Two main PET/MRI integration patterns emerged after analysis of volumetric data: pattern vMRI-in-vPET (11/23) and pattern vPET-in-vMRI (9/23). Besides, a possible third pattern with differences in both directions (vMRI-diff-vPET) could also be observed (3/23). There was a statistically significant association between the tumour classification and integration patterns described above (p < 0.001, κ = 0.72). GBM was associated with pattern vMRI-in-vPET (9/10), low-grade with pattern vPET-in-vMRI (7/8) and anaplastic with pattern vMRI-diff-vPET (3/5).
  
  
  CONCLUSIONS
  The metabolically active tumour volume observed in (11)C-methionine PET differs from the volume of MRI by showing areas of infiltrative tumour and distinguishing from non-tumour lesions. Differences in (11)C-methionine PET/MRI integration patterns can be assigned to tumour grades according to the WHO classification. This finding may improve tumour delineation and therapy planning for gliomas.
authors.affiliation: Department of Nuclear Medicine, Clinica Universidad de Navarra, Avenida Pio XII, 36, 31008 Pamplona, Spain. jarbizu@unav.es
authors.forename: Javier
authors.initials: J
authors.lastname: Arbizu
authors.forename: S
authors.initials: S
authors.lastname: Tejada
authors.forename: J M
authors.initials: JM
authors.lastname: Marti-Climent
authors.forename: R
authors.initials: R
authors.lastname: Diez-Valle
authors.forename: E
authors.initials: E
authors.lastname: Prieto
authors.forename: G
authors.initials: G
authors.lastname: Quincoces
authors.forename: C
authors.initials: C
authors.lastname: Vigil
authors.forename: M A
authors.initials: MA
authors.lastname: Idoate
authors.forename: J L
authors.initials: JL
authors.lastname: Zubieta
authors.forename: I
authors.initials: I
authors.lastname: Peñuelas
authors.forename: J A
authors.initials: JA
authors.lastname: Richter
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D005910:Glioma / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D006801:Humans; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008715:Methionine; D008875:Middle Aged; D060787:Neoplasm Grading; D049268:Positron-Emission Tomography / Q000379:methods*; D013997:Time Factors; D047368:Tumor Burden; D055815:Young Adult
chemical_list: C086242:carbon-11 methionine; D008715:Methionine