Dual-time-point 68Ga-FAPI PET/CT in gastrointestinal malignancies: head-to-head comparison with 18 F-FDG for lesion detection and patient-level assessment

OBJECTIVES: To compare the diagnostic performance of 18 F-Fluorodeoxyglucose (FDG) and 68Ga-fibroblast activation protein inhibitor (FAPI) positron emission tomography/computed tomography (PET/CT) in gastrointestinal malignancies, with particular emphasis on lesion detection, peritoneal disease assessment, and the potential added value of dual-time-point FAPI imaging. METHODS: Thirty-eight patients with histologically confirmed gastrointestinal cancers who underwent both FDG and FAPI PET/CT within a 4-week interval were retrospectively analyzed. FAPI PET/CT images were acquired at 10 and 60 min after tracer injection. Patient-level analyses (staging/restaging accuracy, impact on management) and lesion-based analyses (detection rate, characterization, maximum standardized uptake value [SUVmax] dynamics, lesion size) were evaluated against follow-up data as the reference standard. RESULTS: FAPI PET/CT demonstrated superior agreement with the reference standard compared with FDG PET/CT for staging and restaging (κ = 0.91 vs. 0.32). On lesion-based analysis, FAPI showed markedly higher detection rate for malignant lesions (86% vs. 34%) and fewer indeterminate findings. Median peritoneal carcinomatosis index score and the number of detected malignant lesions per patient were significantly higher with FAPI PET/CT (p < 0.001). Dual-time-point FAPI imaging revealed a significant increase in SUVmax from early to later time points in malignant lesions, whereas benign lesions showed no significant change. Larger lesions (> 10 mm) demonstrated more pronounced delayed uptake, and greater early-to-delayed SUVmax increases were independently associated with malignancy, suggesting a potential role for dynamic uptake patterns in lesion characterization. CONCLUSIONS: Dual-time-point 68Ga-FAPI PET/CT demonstrated superior lesion detectability compared with FDG PET/CT in gastrointestinal malignancies and may help reduce diagnostic uncertainty. These findings suggest that dual-time-point FAPI imaging may provide incremental value for lesion characterization and support its complementary role in oncologic imaging.