Pathological Validation of Functional Imaging in Head and Neck Squamous Cell Carcinoma

Chemo-radiotherapy (CRT) is currently the cornerstone in the management of locoregional advanced head and neck cancer (HNC). Optimization of the quality of RT is therefore an important issue, if the investigators want to improve the therapeutic index in HNC. This could be achieved by a more accurate definition of the tumor volume and by identification of radioresistant volumes within the tumor. Recent literature puts in this regard the incorporation of functional imaging (FI) in the RT treatment planning forward as a promising tool. FI modalities provide an outstanding contrast between tumor and surrounding tissues. This is in contrast to anatomical imaging. Using anatomical imaging in RT treatment planning, sufficient margins need to be placed around the tumor volume in order to compensate for geometric uncertainties. Consequently many surrounding functional structures receive high doses of irradiation, resulting in side effects. It is expected that, using FI in RT treatment planning will make these margins smaller or even unnecessary, which will result in less irradiation of the surrounding tissues. So far only one study has reported a comparison between tumor volume on anatomical (CT and MRI) and FI (PET-CT) modalities with pathological tumor volume. This study showed indeed that the tumor volumes delineated on PET-CT correlated more to tumor volumes defined by pathology and were significantly smaller. Furthermore, FI provides us with a deeper insight in the tumor's underlying biological activity and microstructure. These techniques can thus help to identify radioresistant subvolumes which might benefit from treatment intensification. A validation of these FI modalities with pathology is necessary to investigate their true power in tumor delineation and in the identification of radioresistant subvolumes.