Diffusion-weighted imaging (DWI) is a promising technique for early stratification of responders and non-responders in head and neck chemoradiotherapy. However, data corruption due to swallowing and misalignment reduce the precision of estimated DWI parameters. We investigated different post-processing approaches to improve the reproducibility of the apparent diffusion coefficient (ADC) and demonstrated an improvement in reproducibility from 13.2% to 6.7%. Inter-volume registration showed the largest improvement compared to intra-volume registration and swallowing artifact rejection. The 6.7% reproducibility is sufficient for stratification of responders and non-responders in H&N chemoradiotherapy.