FAPI PET imaging value in radiotherapy planning and assessment in head and neck cancers

Head and neck cancers (HNCs) represent a heterogeneous group of malignancies, predominantly composed of squamous cell carcinoma. Radiotherapy (RT), either alone or concurrently with chemotherapy, remains a central component of definitive and adjuvant treatment in HNCs. The success of radiotherapy depends on precise target volume delineation, which relies heavily on advanced imaging techniques. Positron emission tomography with fluorodeoxyglucose (FDG-PET) is well-established in RT planning workflows and endorsed by international guidelines. Recent advances in molecular imaging using fibroblast activation protein inhibitors (FAPI) targeting PET tracers offer improved tumor visualization and target delineation with early studies demonstrating more distinct tumor margins and improved diagnostic performance compared with FDG PET in HNCs. These advantages align with the critical need for highly reliable imaging in a disease site where complex anatomy complicates RT delivery. Early findings suggest a promising role for FAPI PET, in refining gross tumor volume (GTV) delineation and complementing current RT workflows. Despite the promising findings, current evidence is limited to small, primarily single-center cohorts, some with heterogeneous tumor subtypes, and the absence of prospective outcome-based validation. In addition, the utility of FAPI PET in post-RT response assessment and the optimal timing of imaging has yet to be clear defined. Rigorous, methodologically well-designed prospective studies are needed to establish the clinical value, prognostic significance, and impact of FAPI PET on radiotherapy outcomes in HNCs.