Role and value of diffusion-weighted MRI in the radiotherapeutic management of head and neck cancer

With the association of concurrent chemotherapy, the widespread implementation of altered fractionation schedules and the use of more conformal radiotherapy techniques, the locoregional management of patients with squamous cell carcinoma of the head and neck region (HNSCC) has greatly improved over the last decades. However, associated toxicity has reached the limits of acceptability. If we want to further improve the therapeutic index of HNSCC we will need to target the tumor more accurately while sparing the surrounding organs at risk as much as possible. Therefore, accurate detection and delineation of tumor areas is essential, and diffusion-weighted MRI (DW-MRI) might help us in this task. DW-MRI can characterize tissues and generate image contrast based on differences in water mobility. Thus, while conventional imaging techniques such as computed tomography and MRI depict anatomical structures, functional imaging techniques such as DW-MRI provide us with a deeper insight in the tumor's underlying biological activity and microstructural characteristics. In this article, we aim to bundle the current experience on DW-MRI in HNSCC and elaborate on its potential value and drawbacks at different time points before, during and after radiotherapy.