Head and neck PET/CT therapy response interpretation criteria (Hopkins criteria) - external validation study.

Qualitative assessment of PET/CT results in post therapy is very important to provide a reproducible and systemic reporting. A recently introduced response criteria, known as the Hopkins criteria showed promising results. Our aim is to externally validate the Hopkins interpretation system to assess therapy response in head and neck squamous cell cancer (HNSCC). The study included 69 biopsy proven HNSCC patients who underwent post therapy PET/CT between 5-24 weeks after completion of therapy. PET/CT images were interpreted by one nuclear medicine physician and one nuclear radiologist, independently. The studies were scored according to the Hopkins criteria for right neck, left neck, primary tumor site, and overall assessment. Scores 1, 2, 3 were considered as negative and scores 4 and 5 were considered as positive for tumors. Inter-reader variability was assessed using percent agreement and Kappa statistics. Progression-free survival (PFS) was estimated using the Kaplan-Meier method and analyzed using Cox proportional hazards regression. Of the 69 patients, 59 (85.5%) were males, with a mean age of 62.8 years. The percent agreement between readers for overall, right neck, left neck, and primary tumor site were 91.3%, 97.6%, 97.6%, 91.3% respectively. The sensitivity, specificity, positive predictive value, and negative predictive value of the overall therapy assessment were 66.7%, 87.3%, 33%, 96.5% respectively. Cox univariate regression analysis showed positive primary tumor site scores and overall scores were associated with a higher risk of progression (p<0.05). External validation of Hopkins criteria showed excellent inter-reader agreement and prediction of PFS in HNSCC patients.