Response evaluation after chemoradiotherapy for advanced nodal disease in head and neck cancer using diffusion-weighted MRI and 18F-FDG-PET–CT

Summary Objectives Evaluation of accuracy and interobserver variation of diffusion-weighted magnetic resonance imaging (DW-MRI) and 18F-fluorodeoxyglucose positron emission tomography–computed tomography (18F-FDGPET–CT) to detect residual lymph node metastases after chemoradiotherapy (CRT) in advanced staged head and neck squamous cell carcinoma (HNSCC). Materials and methods Retrospectively, routinely performed DW-MRI ( n = 73) and 18F-FDG-PET–CT ( n = 58) 3 months after CRT in HNSCC-patients with advanced nodal disease (N2–N3) were assessed by two radiologists and two nuclear medicine physicians (individually and in consensus). Imaging was scored dichotomously and on a five-point Likert scale. We also explored different scenarios for the potential added value of DW-MRI to PET–CT using the consensus Likert scale. Histopathology and a follow-up of 9 months after CRT served as reference standard. Results Five patients (7%) had residual regional disease. DW-MRI showed a sensitivity of 60% and a specificity of 93%, vs. 100% and 84% for PET–CT, respectively. DW-MRI and PET–CT observers had ‘moderate’ and ‘substantial’ interobserver agreement ( κ = 0.58 and κ = 0.64, respectively) with the dichotomous system. The combination of PET–CT and DW-MRI showed a sensitivity of 100% and a specificity of 95%. Conclusion The high sensitivity of PET–CT authorizes a neck dissection in all patients with a positive test result and the high specificity of DW-MRI justifies avoidance of invasive neck dissections if the test is negative. Interobserver agreement varied as a function of test positivity criteria. Adding DW-MRI to PET–CT seemed to increase the specificity of PET–CT alone, thereby ensuring that less patients are exposed to unnecessary neck dissections.