Detection of residual head and neck squamous cell carcinoma after (chemo)radiotherapy:a pilot study assessing the value of diffusion-weighted magnetic resonance imaging as an adjunct to PET-CT using 18F-FDG

Objective Diagnosing residual malignancy after (chemo)radiotherapy presents a diagnostic challenge because of overlapping symptoms and imaging characteristics. We assessed the added diagnostic value of diffusion-weighted imaging (DWI) to positron emission tomography combined with computed tomography (PET-CT) in patients with head and neck squamous cell carcinoma (HNSCC) with residual fluorodeoxyglucose (18F-FDG) uptake at the primary tumor site 3 months after (chemo)radiotherapy. Study Design For this retrospective study from January 2010 to June 2012, 22 cases (median patient age of 61 years; range 41-77 years) were included for analysis. Both PET-CT and magnetic resonance imaging (MRI), including DWI, were performed as part of the institutional protocol and were qualitatively assessed for the presence of residual malignancy at the primary tumor site. Results The sensitivity and specificity of PET-CT were 100% and 47%, respectively. For DWI, sensitivity and specificity were 80% and 82%, respectively. When DWI was added to PET-CT with residual 18F-FDG uptake, and only a positive read on both PET-CT and DWI was considered to be overall positive, sensitivity remained 80% (95% confidence interval [CI] 28%-99%), and specificity was 88% (95% CI 64%-99%). Conclusions In this pilot study of the selected patients with residual 18F-FDG uptake at the primary tumor site 3 months after (chemo)radiotherapy, we demonstrated that the addition of DWI to PET-CT has the potential to increase the specificity of the response evaluation with limited decrease in sensitivity.