title: Metabolic tumour volumes measured at staging in lymphoma: methodological evaluation on phantom experiments and patients.
abstract: OBJECTIVE
  The presence of a bulky tumour at staging on CT is an independent prognostic factor in malignant lymphomas. However, its prognostic value is limited in diffuse disease. Total metabolic tumour volume (TMTV) determined on (18)F-FDG PET/CT could give a better evaluation of the total tumour burden and may help patient stratification. Different methods of TMTV measurement established in phantoms simulating lymphoma tumours were investigated and validated in 40 patients with Hodgkin lymphoma and diffuse large B-cell lymphoma.
  
  
  METHODS
  Data were processed by two nuclear medicine physicians in Reggio Emilia and Créteil. Nineteen phantoms filled with (18)F-saline were scanned; these comprised spherical or irregular volumes from 0.5 to 650 cm(3) with tumour-to-background ratios from 1.65 to 40. Volumes were measured with different SUVmax thresholds. In patients, TMTV was measured on PET at staging by two methods: volumes of individual lesions were measured using a fixed 41% SUVmax threshold (TMTV41) and a variable visually adjusted SUVmax threshold (TMTVvar).
  
  
  RESULTS
  In phantoms, the 41% threshold gave the best concordance between measured and actual volumes. Interobserver agreement was almost perfect. In patients, the agreement between the reviewers for TMTV41 measurement was substantial (ρ c = 0.986, CI 0.97 - 0.99) and the difference between the means was not significant (212 ± 218 cm(3) for Créteil vs. 206 ± 219 cm(3) for Reggio Emilia, P = 0.65). By contrast the agreement was poor for TMTVvar. There was a significant direct correlation between TMTV41 and normalized LDH (r = 0.652, CI 0.42 - 0.8, P <0.001). Higher disease stages and bulky tumour were associated with higher TMTV41, but high TMTV41 could be found in patients with stage 1/2 or nonbulky tumour.
  
  
  CONCLUSIONS
  Measurement of baseline TMTV in lymphoma using a fixed 41% SUVmax threshold is reproducible and correlates with the other parameters for tumour mass evaluation. It should be evaluated in prospective studies.
authors.affiliation: Department of Nuclear Medicine, Hôpital Henri Mondor and Paris-Est University, Créteil, France, michel.meignan@hmn.aphp.fr.
authors.forename: Michel
authors.initials: M
authors.lastname: Meignan
authors.forename: Myriam
authors.initials: M
authors.lastname: Sasanelli
authors.forename: René Olivier
authors.initials: RO
authors.lastname: Casasnovas
authors.forename: Stefano
authors.initials: S
authors.lastname: Luminari
authors.forename: Federica
authors.initials: F
authors.lastname: Fioroni
authors.forename: Chiara
authors.initials: C
authors.lastname: Coriani
authors.forename: Helene
authors.initials: H
authors.lastname: Masset
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Itti
authors.forename: Paolo G
authors.initials: PG
authors.lastname: Gobbi
authors.forename: Francesco
authors.initials: F
authors.lastname: Merli
authors.forename: Annibale
authors.initials: A
authors.lastname: Versari
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D019788:Fluorodeoxyglucose F18; D006689:Hodgkin Disease / Q000000981:diagnostic imaging* / Q000473:pathology; D006801:Humans; D016403:Lymphoma, Large B-Cell, Diffuse / Q000000981:diagnostic imaging* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging / Q000295:instrumentation; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000295:instrumentation*; D019275:Radiopharmaceuticals; D014057:Tomography, X-Ray Computed / Q000295:instrumentation; D047368:Tumor Burden
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18