Interim ¹⁸F-FDG PET/CT During Chemoradiation Therapy in the Management of Head and Neck Cancer Patients: A Systematic Review

Positron emission tomography (PET) is an imaging modality widely applied in oncology for tumor staging, volume delineation in radiation therapy planning, and therapy response assessment. F-18 fluorodeoxyglucose (FDG) PET combined with computed tomography plays a significant role in the management of locally advanced head and neck cancer patients in the pretreatment setting to predict outcome and prognosis and after chemoradiation therapy (CRT) to assess tumor response. This review aims to evaluate the use of FDG PET acquired during CRT, ad interim FDG (FDG_int), to identify tumor response at an early stage, modify the treatment plan if necessary, or set up alternative strategies to enhance the therapeutic ratio. Most of the studies confirmed the value of FDG_int in predicting the response to CRT, whereas a few highlighted the poor predictive value of FDG_int compared with FDG acquired 2 to 4 months after the end of CRT, which was well correlated with local and regional control and survival. Such findings deserve to be further analyzed in more homogeneous series with greater patient numbers according to the tumor site and CRT schedules. The best time to assess tumor response during radiation therapy remains a matter of debate, although 2 weeks seems most favorable, still providing the opportunity to adapt the treatment strategy.