Comparative analysis of two timepoints on [¹⁸F]FAPI-42 PET/CT in various cancers

Purpose: This study aimed to assess the biodistribution, detection rate, and uptake of the [¹⁸F]FAPI-42 at two distinct time intervals.

Methods: This prospective study enrolled 60 consecutive patients (median age 59; range 35-74) referred to [¹⁸F]FAPI-42 PET/CT. [¹⁸F]FAPI-42 PET/CT was performed early and late timepoint after tracer injection for staging or restaging. Positive lesions specified for anatomic locations (primary or recurrent tumor, LN metastasis and other metastasis) by visual analysis at both timepoints. Semiquantitative analysis of the tracer activity in lesions as well as normal tissues at both time points were measured and compared. In a subgroup analysis, eleven patients underwent 2-[¹⁸F]FDG PET/CT within 1 week, the detection rate and uptake of lesion were compared between early [¹⁸F]FAPI-42 and 2-[¹⁸F]FDG.

Results: Uptake of [¹⁸F]FAPI-42 in the late timepoint was significantly lower than the early timepoint in most organs (all p < 0.05), except for bone (SUV_mean 0.88 vs. 0.85; p = 0.218). Tracer retention at biliary system showed less frequent at early timepoint than late timepoint. A total of 194 lesions were detected in 60 patients. One lesion was only seen at early timepoint but not at late timepoint. Lesions on early [¹⁸F]FAPI-42 PET/CT had higher visual score than that of late image(23 vs. 6). The uptake of lesion decreased significantly from early to late timepoint (all p < 0.05). In subgroup analysis, early [¹⁸F]FAPI-42 illustrated higher detection rate, visual score, and uptake of lesion than that of 2-[¹⁸F]FDG PET/CT.

Conclusion: Early [¹⁸F]FAPI-42 PET/CT provided consistent detection rates and lesion uptake, but less tracer retention in the biliary system compared to late images. Therefore, acquisition at early timepoint could be a feasible strategy for improving acquisition protocols of [¹⁸F]FAPI-42 PET/CT.

Trial registration: ChiCTR2200063441. Registered 28 September 2022-Retrospectively registered, https://www.chictr.org.cn/bin/project/edit?pid=149714 .