Abstract
Most of patients with head and neck cancers (HNC) need curative radiotherapy either as radical treatment or in the postoperative adjuvant setting. Accurate target definition is paramount to ensure a good outcome of radiotherapy. Pretreatment Computed Tomography (CT) is regularly performed for radiation therapy planning, which both guides dose calculation and aids accurately contouring the tumor volume. Nevertheless, when using CT, the low resolution of soft- tissue and the dental artifacts may render the primary tumor identification difficult. The interobserver inconsistency on the definition of the radiation target volume is additionally a generally perceived issue. With the increase of the frequency of HNC treatment by Intensity-modulated radiotherapy (IMRT), the accurate target volume delineation performed by using Fluorodeoxy D-glucose positron emission tomography combined to CT (FDG-PET/CT) had become even more significant. Nevertheless, the ideal technique for precisely deciding the exact margins and form of the biologic tumor volume (BTV) remains challenging. FDG-PET/CT can define BTVs either for escalation of dose or alternative treatment strategies. Debatable issues still exist on the role of FDG PET/CT during radiotherapy treatment. Moreover, some new PET tracers, other than FDG, have been investigated for imaging specific biologic tumor characteristics in HNC. The purpose of this narrative review is to discuss the use of FDG-PET/CT for BTV definition before and during delivery of radiotherapy for HNC with attention to PET tracers other than FDG.

Key words: FDG-PET/CT, Biologic target volume, Head and neck cancer, Radiotherapy planning.