Background <p>Cancer associated fibroblasts have become a target of interest in different malignancies for positron emission tomography (PET) imaging, using positron emitter labelled fibroblast activation protein inhibitors (FAPI). New data underline the advanced imaging properties of FAPI-PET/CT for the staging of esophageal cancer compared to standard imaging. Potential benefits of FAPI-PET/CT in radiation therapy planning are the subject of this investigation.</p> Methods <p>Ten patients with newly diagnosed esophageal cancer treated with radiochemotherapy (RCT) were retrospectively analyzed. All patients underwent [68Ga]OncoFAP-PET/CT in treatment position to facilitate radiation treatment planning. Six patients received neoadjuvant RCT as part of a trimodal therapy and four patients underwent definitive RCT. In five cases, restaging after initial treatment was performed with FAPI-PET/CT.</p> Results <p>[68Ga]OncoFAP-PET/CT based imaging showed a high correlation with the endoscopic staging for initial imaging. In three cases, new sites of disease were unmasked, not visible in CT- and endosonographic staging. [68Ga]OncoFAP-PET/CT based RT delineation offered good definition of clinical target volumes, especially in retro-/paracardial areas and the gastroesophageal junction.</p> Conclusion <p>[68Ga]OncoFAP-PET/CT may aid and improve radiation treatment planning for patients with esophageal cancer.</p>