Zhao_2021_Radiother.Oncol_158_55

BACKGROUND AND PURPOSE: To compare (68)Ga-fibroblast activation protein inhibitor (FAPI) and (18)F-FDG PET/CT in imaging locally advanced oesophageal cancer, and evaluate the potential usefulness of (68)Ga-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 (18)F-FDG PET/CT. MATERIALS AND METHODS: Twenty-one patients with newly diagnosed oesophageal cancer who underwent both (18)F-FDG and (68)Ga-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 (68)Ga-FAPI PET showed significantly higher radiotracer uptake than (18)F-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 (68)Ga-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.