title: Delayed response assessment with FDG-PET-CT following (chemo) radiotherapy for locally advanced head and neck squamous cell carcinoma.
abstract: OBJECTIVE
  To analyse the diagnostic accuracy of delayed response assessment 2-[¹⁸F]-fluoro-2-deoxy-d-glucose (FDG) positron-emission tomography-computed tomography (PET-CT) following (chemo)radiation for locally advanced head and neck squamous cell carcinoma (HNSCC).
  
  
  METHODS
  Forty-four consecutive patients who underwent a baseline and response assessment using FDG PET-CT for HNSCC following (chemo)radiation between August 2008 and April 2011 were identified retrospectively. Clinicopathological findings and serial clinical follow-up provided the reference standard.
  
  
  RESULTS
  Median follow-up was 14 months (range 5-43 months). Response assessment FDG PET-CT was performed at 16.8 weeks (inter-quartile range 15.8-18.6 weeks). Thirty-one out of 44 (70%) response assessment examinations showed a complete metabolic response. Seven out of 40 (18%) assessable primary tumours were positive. Eight out of 41 (20%) patients with pre-treatment nodal disease had equivocal or positive FDG uptake at response assessment. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for primary disease and nodal disease were 100, 89, 43, 100, and 100%, and 92, 63, and 100%, respectively. Seven patients had residual FDG-negative soft tissue detectable on the unenhanced CT component of the response assessment images; all remained disease free after clinical observation. Distant metastases were detected on response assessment FDG PET-CT in four out of the 44 patients (10%).
  
  
  CONCLUSIONS
  The diagnostic accuracy of response assessment with FDG PET-CT performed at approximately 16 weeks post-(chemo)radiotherapy is good. The very high NPV of a complete metabolic response can be used to guide management decisions. Although the PPV is limited for local residual disease, FDG PET-CT is a powerful screening tool for the detection of interim metastatic disease.
authors.affiliation: Department of Nuclear Medicine, St James's Institute of Oncology, Leeds, UK. Robin.Prestwich@leedsth.nhs.uk
authors.forename: R J D
authors.initials: RJ
authors.lastname: Prestwich
authors.forename: M
authors.initials: M
authors.lastname: Subesinghe
authors.forename: A
authors.initials: A
authors.lastname: Gilbert
authors.forename: F U
authors.initials: FU
authors.lastname: Chowdhury
authors.forename: M
authors.initials: M
authors.lastname: Sen
authors.forename: A F
authors.initials: AF
authors.lastname: Scarsbrook
mesh_terms: D000328:Adult; D000368:Aged; D002294:Carcinoma, Squamous Cell / Q000175:diagnosis* / Q000628:therapy*; D059248:Chemoradiotherapy; D057210:Delayed Diagnosis; D005260:Female; D019788:Fluorodeoxyglucose F18; D006258:Head and Neck Neoplasms / Q000175:diagnosis* / Q000628:therapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging / Q000379:methods*; D049268:Positron-Emission Tomography; D011379:Prognosis; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18