Value of [18F]AlF-NOTA-FAPI-04 PET/CT for differential diagnosis of malignant and various inflammatory lung lesions: comparison with [18F]FDG PET/CT

Uptake of the imaging tracers [18F]AlF-NOTA-FAPI-04 and [18F]FDG varies in some inflammatory lesions, which may result in false-positive findings for malignancy on PET/CT. Our aim was to compare the [18F]AlF-NOTA-FAPI-04 and [18F]FDG PET/CT imaging features of malignant and various inflammatory lung lesions and to analyze their value for differential diagnosis. We retrospectively analyzed [18F]AlF-NOTA-FAPI-04 PET/CT scans from 67 cancer patients taken between December 2020 and January 2022, as well as the scans of 32 patients who also underwent [18F]FDG PET/CT imaging. The maximum and mean standardized uptake values (SUVmax and SUVmean, respectively) and lesion-to-background ratio (LBR) were calculated. The predictive capabilities of semiquantitative PET/CT parameters were analyzed by receiver operating characteristic curve analysis. A total of 70 inflammatory and 37 malignant lung lesions were evaluated by [18F]AlF‑NOTA‑FAPI‑04 PET/CT, and 33 inflammatory and 26 malignant lung lesions also were evaluated by [18F]FDG PET/CT. Inflammatory lesions exhibited lower [18F]AlF-NOTA-FAPI-04 and [18F]FDG uptake compared to malignant lesions, with statistically significant differences in SUVmax, SUVmean, and LBR (all p < 0.001). [18F]AlF-NOTA-FAPI-04 uptake also varied among different types of inflammatory lesions (SUVmax, p = 0.005; SUVmean, p = 0.008; LBR, p < 0.001), with the highest uptake observed in bronchiectasis with infection, followed by postobstructive pneumonia, and the lowest in pneumonia. [18F]FDG uptake was higher in postobstructive pneumonia than in pneumonia (SUVmax, p = 0.009; SUVmean, p = 0.016; LBR, p = 0.004). [18F]AlF-NOTA-FAPI-04/[18F]FDG PET/CT showed significantly lower uptake in inflammatory lesions than malignancies as well as variation in different types of inflammatory lesions, and thus, may be valuable for distinguishing malignant and various inflammatory findings. Our study confirmed that the uptake of [18F]AlF-NOTA-FAPI-04/[18F]FDG PET/CT in inflammatory and malignant lung lesions is different, which is beneficial to distinguish inflammatory and malignant lung lesions in clinic. • Malignant and different inflammatory lung lesions showed varying degrees of uptake of [18F]AlF-NOTA-FAPI-04 and [18F]FDG. • Inflammatory lung lesions showed significantly less uptake than malignancies, and uptake varied among different types of inflammatory lesions. • Both types of PET/CT could differentiate malignant and various inflammatory lung findings.