title: Assessment of tumor volumes in skull base glomus tumors using Gluc-Lys[(18)F]-TOCA positron emission tomography.
abstract: OBJECTIVE
  To assess a threshold for Gluc-Lys[(18)F]-TOCA positron emission tomography (PET) in target volume delineation of glomus tumors in the skull base and to compare with MRI-based target volume delineation.
  
  
  METHODS
  The threshold for volume segmentation in the PET images was determined by a phantom study. Nine patients with a total of 11 glomus tumors underwent PET either with Gluc-Lys[(18)F]-TOCA or with (68)Ga-DOTATOC (in 1 case). All patients were additionally scanned by MRI. Positron emission tomography and MR images were transferred to a treatment-planning system; MR images were analyzed for lesion volume by two observers, and PET images were analyzed by a semiautomated thresholding algorithm.
  
  
  RESULTS
  Our phantom study revealed that 32% of the maximum standardized uptake value is an appropriate threshold for tumor segmentation in PET-based target volume delineation of gross tumors. Target volume delineation by MRI was characterized by high interobserver variability. In contrast, interobserver variability was minimal if fused PET/MRI images were used. The gross tumor volumes (GTVs) determined by PET (GTV-PET) showed a statistically significant correlation with the GTVs determined by MRI (GTV-MRI) in primary tumors; in recurrent tumors higher differences were found. The mean GTV-MRI was significantly higher than mean GTV-PET. The increase added by MRI to the common volume was due to scar tissue with strong signal enhancement on MRI.
  
  
  CONCLUSIONS
  In patients with glomus tumors, Gluc-Lys[(18)F]-TOCA PET helps to reduce interobserver variability if an appropriate threshold for tumor segmentation has been determined for institutional conditions. Especially in patients with recurrent tumors after surgery, Gluc-Lys[(18)F]-TOCA PET improves the accuracy of GTV delineation.
authors.affiliation: Klinik für Strahlentherapie und Radiologische Onkologie, Klinikum rechts der Isar der Technischen Universität München, Munich, Germany.
authors.forename: Sabrina T
authors.initials: ST
authors.lastname: Astner
authors.forename: Ralph A
authors.initials: RA
authors.lastname: Bundschuh
authors.forename: Ambros J
authors.initials: AJ
authors.lastname: Beer
authors.forename: Sibylle I
authors.initials: SI
authors.lastname: Ziegler
authors.forename: Bernd J
authors.initials: BJ
authors.lastname: Krause
authors.forename: Markus
authors.initials: M
authors.lastname: Schwaiger
authors.forename: Michael
authors.initials: M
authors.lastname: Molls
authors.forename: Anca L
authors.initials: AL
authors.lastname: Grosu
authors.forename: Markus
authors.initials: M
authors.lastname: Essler
mesh_terms: D005632:Fructose / Q000031:analogs & derivatives*; D005918:Glomus Tumor / Q000000981:diagnostic imaging* / Q000473:pathology; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D009364:Neoplasm Recurrence, Local / Q000175:diagnosis / Q000000981:diagnostic imaging; D015588:Observer Variation; D015282:Octreotide / Q000031:analogs & derivatives; D009942:Organometallic Compounds; D010456:Peptides, Cyclic; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals; D019292:Skull Base Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology; D047368:Tumor Burden
chemical_list: C499142:Ga(III)-DOTATOC; C475998:N(alpha)-(1-deoxy- D-fructosyl)- N(epsilon)-(2-fluoropropionyl)-Lys(0)-Tyr(3)-octreotate; D009942:Organometallic Compounds; D010456:Peptides, Cyclic; D019275:Radiopharmaceuticals; D005632:Fructose; D015282:Octreotide