The ability of post-chemoradiotherapy DWI ADC mean and 18 F-FDG SUV max to predict treatment outcomes in head and neck cancer: impact of human papilloma virus oropharyngeal cancer status

Objectives To evaluate the ability of post-chemo-radiotherapy (CRT) diffusion-weighted-MRI apparent diffusion coefficient (ADC mean ) and 18 F-FDG PET maximum standardized uptake value (SUV max ) to predict disease-free survival (DFS) in head and neck squamous cell carcinoma (HNSCC), and to determine whether this ability is influenced by human papillomavirus oropharyngeal cancer (HPV-OPC) status. Methods This prospective cohort observational study included 65 participants (53 male, mean ± SD age 59.9 ± 7.9 years, 46 HPV-OPC) with stage III or IV HNSCC. Primary tumour and nodal ADC mean (pre-treatment, 6- and 12-weeks post-CRT) and SUV max (12-weeks post-CRT) were measured. Variables were compared with 2-year DFS (independent t -test/Mann–Whitney test) and overall DFS (Cox regression), before and after accounting for HPV-OPC status. Variables were also compared between HPV-OPC and other HNSCC subgroups after stratifying for DFS. Results Absolute post-CRT ADC mean values predicted 2-year DFS and overall DFS for all participants ( p = 0.03/0.03, 6-week node; p = 0.02/0.03 12-week primary tumour) but not in the HPV-OPC subgroup. In participants with DFS, percentage interval changes in primary tumour ADC mean at 6- and 12-weeks were higher in HPV-OPC than other HNSCC ( p = 0.01, 6 weeks; p = 0.005, 12 weeks). The 12-week post-CRT SUV max did not predict DFS. Conclusion Absolute post-CRT ADC mean values predicted DFS in HNSCC but not in the HPV-OPC subgroup. Amongst participants with DFS, post-CRT percentage interval changes in primary tumour ADC mean were significantly higher in HPV-OPC than in other HNSCC. Knowledge of HPV-OPC status is crucial to the clinical utilisation of post-CRT DWI-MRI for the prediction of outcomes.