title: Can FDG-PET assist in radiotherapy target volume definition of metastatic lymph nodes in head-and-neck cancer?
abstract: OBJECTIVE
  The role of FDG-PET in radiotherapy target volume definition of the neck was evaluated by comparing eight methods of FDG-PET segmentation to the current CT-based practice of lymph node assessment in head-and-neck cancer patients.
  
  
  METHODS
  Seventy-eight head-and-neck cancer patients underwent coregistered CT- and FDG-PET scans. Lymph nodes were classified as "enlarged" if the shortest axial diameter on CT was 10mm, and as "marginally enlarged" if it was 7-10mm. Subsequently, lymph nodes were assessed on FDG-PET applying eight segmentation methods: visual interpretation (PET(VIS)), applying fixed thresholds at a standardized uptake value (SUV) of 2.5 and at 40% and 50% of the maximum signal intensity of the primary tumor (PET(SUV), PET(40%), PET(50%)) and applying a variable threshold based on the signal-to-background ratio (PET(SBR)). Finally, PET(40%N), PET(50%N) and PET(SBRN) were acquired using the signal of the lymph node as the threshold reference.
  
  
  RESULTS
  Of 108 nodes classified as "enlarged" on CT, 75% were also identified by PET(VIS), 59% by PET(40%), 43% by PET(50%) and 43% by PET(SBR). Of 100 nodes classified as "marginally enlarged", only a minority were visualized by FDG-PET. The respective numbers were 26%, 10%, 7% and 8% for PET(VIS), PET(40%), PET(50%) and PET(SBR). PET(40%N), PET(50%N) and PET(SBRN), respectively, identified 66%, 82% and 96% of the PET(VIS)-positive nodes.
  
  
  CONCLUSIONS
  Many lymph nodes that are enlarged and considered metastatic by standard CT-based criteria appear to be negative on FDG-PET scan. Alternately, a small proportion of marginally enlarged nodes are positive on FDG-PET scan. However, the results are largely dependent on the PET segmentation tool used, and until proper validation FDG-PET is not recommended for target volume definition of metastatic lymph nodes in routine practice.
authors.affiliation: Department of Radiation Oncology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands. d.schinagl@rther.umcn.nl
authors.forename: Dominic A X
authors.initials: DA
authors.lastname: Schinagl
authors.forename: Aswin L
authors.initials: AL
authors.lastname: Hoffmann
authors.forename: Wouter V
authors.initials: WV
authors.lastname: Vogel
authors.forename: Jorn A
authors.initials: JA
authors.lastname: van Dalen
authors.forename: Suzan M M
authors.initials: SM
authors.lastname: Verstappen
authors.forename: Wim J G
authors.initials: WJ
authors.lastname: Oyen
authors.forename: Johannes H A M
authors.initials: JH
authors.lastname: Kaanders
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D019788:Fluorodeoxyglucose F18; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology* / Q000532:radiotherapy; D006801:Humans; D008207:Lymphatic Metastasis / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D011446:Prospective Studies; D019275:Radiopharmaceuticals; D018709:Statistics, Nonparametric; D014055:Tomography, Emission-Computed; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18