Comparison of physiological uptake of normal tissues in patients with cancer using 18F-FAPI-04 and 18F-FAPI-42 PET/CT.

Abstract

Purpose: To calculate the physiological uptake of various tissues in patients with cancer using ¹⁸F-AlF-NOTA-FAPI-04 (¹⁸F-FAPI-04) and ¹⁸F-AlF-NOTA-FAPI-42 (¹⁸F-FAPI-42) PET/CT and to compare the variation in standard uptake values between the two scans.

Materials and methods: This retrospective analysis included 40 patients with cancer who underwent ¹⁸F-FAPI; the first 20 patients received ¹⁸F-FAPI-04 PET/CT and the remaining 20 patients received ¹⁸F-FAPI-42 PET/CT. A total of 49 normal tissues, including the brain (cerebrum/cerebellum), parotid and submandibular glands, palatine tonsils, and thyroid, were identified on CT images. For these normal tissues, maximum standardized uptake value (SUVmax) and mean standardized uptake value (SUVmean) were calculated. We also compared the SUVmean of identical tissues to explore the difference in biodistribution between the two radiotracers.

Results: The accumulation of ¹⁸F-FAPI-04 and ¹⁸F-FAPI-42 showed an analogous pattern. High uptake of both radiotracers in the gallbladder, uterus, submandibular gland, and renal pelvis was demonstrated (range: SUVmax, 4.01-5.75; SUVmean, 2.92-4.22). Furthermore, the uptake of bony tissues was slightly higher in ¹⁸F-FAPI-42 than in ¹⁸F-FAPI-04 (range: SUVmean, 0.4 ± 0.22-0.9 ± 0.34 and 0.3 ± 0.24-0.7 ± 0.18, respectively, p < 0.05), while the uptake of some soft tissues was higher in ¹⁸F-FAPI-04 than in ¹⁸F-FAPI-42 (range: SUVmean, 0.9 ± 0.24-1.5 ± 0.35 and 0.9 ± 0.26-1.2 ± 0.37, respectively, p < 0.05).

Conclusions: Both radioligands exhibited similar physiological uptake of normal tissues in patients with cancers. In addition, ¹⁸F-FAPI-42 demonstrated higher uptake of bone tissues than ¹⁸F-FAPI-04 while showing lower uptake of soft tissues than ¹⁸F-FAPI-04.