title: Role of 11-C-methionine positron emission tomography for the delineation of the tumor volume in pharyngo-laryngeal squamous cell carcinoma: comparison with FDG-PET and CT.
abstract: OBJECTIVE
  Although computed tomography (CT) remains the imaging modality of reference in head and neck squamous cell carcinoma (HNSCC) for the three-dimensional (3D) conformal radiotherapy, its poor soft tissue contrast can hamper precisely delineate the tumor volume. Besides anatomical imaging, 2-[18F] fluoro-2-deoxy-d-glucose-positron emission tomography (FDG-PET) has been shown to enhance the accuracy of the tumor delineation but l-methyl [11C]-methionine-positron emission tomography (MET-PET) has never been tested for this purpose. This study was undertaken to determine the potential added value of MET-PET for the delineation of gross target volume (GTV) in HNSCC, as compared to CT and FDG-PET.
  
  
  METHODS
  Twenty-three patients (10 oropharynx, 8 larynx and 5 hypopharynx) presenting with stage II-IV HNSCC were prospectively enrolled. They were treated by primary radiotherapy or by total laryngectomy. Images (CT, FDG-PET and MET-PET) were acquired with a thermoplastic mask and after coregistration, tumor volumes were delineated on CT and using an adaptative threshold-based automatic method on FDG- and MET-PET. Absolute volumes as well as the mismatch between modalities were compared.
  
  
  RESULTS
  For oropharyngeal lesions, FDG volumes were significantly smaller (19.43 ml+/-21.36) than CT (29.04 ml+/-30.97) (P=0.013). On the other hand, MET volumes (24.36 ml+/-20.59) were not different from CT volumes. Similar results were found for laryngeal and hypopharyngeal tumors, with volume of 24.93 ml+/-19.02 for CT, 21.84 ml+/-15.32 for MET-PET and 14.49 ml+/-11.3 for FDG-PET (P=0.003). Large mismatches were observed between modalities, in particular between CT and PET.
  
  
  CONCLUSIONS
  Our study confirms that the use of FDG-PET may result in a significant reduction of GTV's as compared to CT. On the contrary, MET-PET does not have any additional value since MET volumes are not different from CT volumes, probably because of the high uptake of MET by the normal mucosa and salivary glands surrounding the tumor.
authors.affiliation: Department of Radiotherapy, Cliniques Universitaires Saint-Luc, UCL Medical School, Avenue Hippocrate 10, B-1200 Brussels, Belgium.
authors.forename: Xavier
authors.initials: X
authors.lastname: Geets
authors.forename: Jean-Francois
authors.initials: JF
authors.lastname: Daisne
authors.forename: Vincent
authors.initials: V
authors.lastname: Gregoire
authors.forename: Marc
authors.initials: M
authors.lastname: Hamoir
authors.forename: Max
authors.initials: M
authors.lastname: Lonneux
mesh_terms: D002294:Carcinoma, Squamous Cell / Q000000981:diagnostic imaging*; D005069:Evaluation Studies as Topic; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007822:Laryngeal Neoplasms / Q000000981:diagnostic imaging*; D008279:Magnetic Resonance Imaging; D008715:Methionine / Q000031:analogs & derivatives*; D010610:Pharyngeal Neoplasms / Q000000981:diagnostic imaging*; D011446:Prospective Studies; D019275:Radiopharmaceuticals; D018709:Statistics, Nonparametric; D014055:Tomography, Emission-Computed; D014057:Tomography, X-Ray Computed
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D008715:Methionine; C038344:methionine methyl ester