ESTRO 2024 - Abstract Book

S2284

Clinical - Upper GI

ESTRO 2024

3183

Mini-Oral

Impact of FAPI PET/CT on radiotherapeutic management of esophageal cancer

Simone Wegen 1 , Karina Claus 1 , Philipp Linde 1 , Johannes Rosenbrock 1 , Maike Trommer 1,2 , Thomas Zander 3,4 , Armin Tuchscherer 3,4 , Christiane Bruns 5 , Hans Schlößer 5 , Wolfgang Schröder 5 , Marie-Lisa Eich 6 , Thomas Fischer 7 , Klaus Schomäcker 7 , Alexander Drzezga 7,8 , Carsten Kobe 7 , Katrin Sabine Roth 7 , Jasmin Josefine Weindler 7 1 Faculty of Medicine and University Hospital Cologne, Department of Radiation Oncology, Cyberknife and Radiotherapy, Cologne, Germany. 2 Olivia Newton-John Cancer Wellness & Research Centre, Austin Health, Department of Radiation Oncology, Melbourne, Australia. 3 Faculty of Medicine and University Hospital, University of Cologne, Department I of Internal Medicine, Cologne, Germany. 4 Faculty of Medicine and University Hospital Cologne, Center for Integrated Oncology, Cologne, Germany. 5 Faculty of Medicine and University Hospital Cologne, Department of General, Visceral, Cancer and Transplantation Surgery, Cologne, Germany. 6 Faculty of Medicine and University Hospital Cologne, Institute of Pathology, Cologne, Germany. 7 Faculty of Medicine and University Hospital Cologne, Department of Nuclear Medicine, Cologne, Germany. 8 Forschungszentrum Jülich, INM-2, Institute of Neuroscience and Medicine, Molecular Organization of the Brain, Cologne, Germany

Purpose/Objective:

Fibroblast activation protein (FAP) is expressed in the tumor microenvironment (TME) of various cancers. We aim to describe the impact of dual-tracer imaging with radiolabeled inhibitors of FAP (FAPI-46-PET/CT) and fluorodeoxy-D glucose (FDG-PET/CT) on the radiotherapeutic management of esophageal cancer (EC).

Material/Methods:

32 patients with EC received FDG and FAPI-46 PET/CT on the same day (dual-tracer protocol, 71%) or on two separate days (29%). We compared functional tumor volumes (FTV) and gross tumor volumes (GTV) in ml and defined cN-/cM- tumor stages between FDG and FAPI PET/CT. Any management changes were categorized as “minor” (adaption/enlargement of radiation field) or “major” (change of treatment regimen). Immunohistochemistry (IHC) staining for FAP was performed in all patients with available tissue.

Results:

Primary tumor was detected in all FAPI-46 scans and in 30/32 (94%) of FDG scans. Most FTVs were larger on both dual-tracer PET/CT (p=0.027) and FAPI-46 PET/CT (p=0.028) compared to FDG PET/CT alone. Compared to the initial staging CT scan, 12/32 patients (38%) were upstaged in nodal status after the combination of FDG and FAPI-46 PET scans. 10/12 lesions were equally visible in both modalities (FDG and FAPI/dual tracer-PET). Compared to initial staging CT, dual tracer PET led to changes in N-stage in 12/32 patients. Three metastatic lymph nodes were visible in FAPI-46/dual-tracer only. PET scans revealed new distant metastasis (biopsy-proven M1) in 2/32 (6%) patients in the PET with FAPI- 46. Our findings led to larger RT fields (“minor change”) in 5/32 patients (16%) and changing treatment regimen (“major change”) in 3/32 patients (9%) (see Figure 1 ).