68Ga-fibroblast activation protein inhibitor PET/CT on gross tumour volume delineation for radiotherapy planning of oesophageal cancer

Background and purpose: To compare Ga-68-fibroblast activation protein inhibitor (FAPI) and F-18-FDG PET/ CT in imaging locally advanced oesophageal cancer, and evaluate the potential usefulness of Ga-68-FAPI PET/CT on gross target volume (GTV) delineation aimed at radiotherapy planning for oesophageal cancer as compared with contrast-enhanced CT (CE-CT) and F-18-FDG PET/CT. Materials and methods: Twenty-one patients with newly diagnosed oesophageal cancer who underwent both F-18-FDG and Ga-68-FAPI PET/CT scans were selected. GTVs of the primary tumours based on CE-CT (GTV(CT)), PET/CT, and CE-CT plus PET/CT were delineated. Gross tumour lengths were measured by GTVs and endoscopy and recorded. Results: The Ga-68-FAPI PET showed significantly higher radiotracer uptake than F-18-FDG PET (median SUVmax 16.71 vs. 11.23; P = 0.002) in the primary tumours. SUV thresholds of FAPI x20%, 30%, 40%, and FDG x40% showed similar lesion lengths compared with that in endoscopic examination (P > 0.05). GTV(CT) demonstrated the largest volume (median: 48.80 mm(3), range: 14.83-162.23 mm(3)) than PET-based GTVs. For PET/CT-guided complementary contouring of GTV(CT), four patients (19%) were increased by FAPI x20% and 30%, two patients (9.5%) were increased by FAPI x40%, and only one patient was increased by FDG x40%. Furthermore, the volume of GTV based on CE-CT plus FAPI x20%, 30%, and 40% showed no significant difference with GTV(CT) and planning target volume based CE-CT plus FAPI-PET and meets the organ at risk standard. Conclusion: The Ga-68-FAPI PET/CT methodology showed favourable tumour-to-background contrast in oesophageal cancer and might provide additional information for target volume delineation and help avoid tumour geographic misses. (C) 2021 The Authors. Published by Elsevier B.V.

Automated summary

This study compared Ga-68-FAPI and F-18-FDG PET/CT in imaging locally advanced esophageal cancer and evaluated the potential usefulness of Ga-68-FAPI PET/CT in radiotherapy planning. Ga-68-FAPI PET showed significantly higher radiotracer uptake in primary tumors compared to F-18-FDG PET, suggesting its advantage in target volume delineation.