Biodistribution, radiation dosimetry and tumor detection of ¹⁸ F-AlF-labeled FAPI-PET/CT in lung cancer patients

Ziel/Aim ⁶⁸Ga-labeled FAPI-04 was reported a promising tracer for imaging several tumor-entities. To overcome supply limitations of short half-life generator nuclide ⁶⁸Ga (T_1/2 68 min) with longer half-life cyclotron produced ¹⁸F (T_1/2 110 min), the preclinical favorable precursor FAPI-74 was labeled with [¹⁸F]AlF (Aluminium-Fluoride) by complexation with the NOTA-moiety of ligand.

Methodik/Methods FAPI-PET/CT using mean 260 MBq (Min: 200/Max: 291) Al¹⁸F-FAPI-74 was acquired at 10 min, 1h and 3h after tracer administration in 10 patients with lung cancer and were evaluated with the QDOSE software to approximate the radiation burden of such an exam. In all patients, normal organ distribution and tumor uptake were semi-quantitatively evaluated per SUV at each time-point. Secondly, automatic target volume delineation of primary tumor lesions based on different FAPI thresholds was performed and dimensions were compared with CT based volumes.

Ergebnisse/Results In primary lung cancer the average SUV_max was 11.8 at 10 min; 12.7 at 1h and 11.3 at 3h; in lymph node metastases it was 9.9, 10.7, and 9.4; in distant metastases 11.8, 11.9 and 11.4. So, for most lesions the uptake peaked later than 10 min. p.i. but there was already some wash-out between 1h and 3h p.i. The effective dose of [¹⁸F]AlF-FAPI-74 was mean 1.3 E-02 mSv/MBq translating into doses of 3-3.5 mSv for an 250 MBq exam. FAPI based target delineation resulted in significantly different volumes 46.7ml/69.3 % and 30.6ml/45,4 % relative increase compared to CT based contouring.

Schlussfolgerungen/Conclusions Due to rapid kidney clearance of non-tumor-bound tracer and moderate unspecific uptake in normal organs, the radiation burden of a diagnostic [¹⁸F]AlF-FAPI-74 PET-scan is even less than with ¹⁸F-FDG or ¹⁸F-PSMA-1007. Pharmacokinetics and tumor-delineation of [¹⁸F]AlF-labeled FAPI-74 is comparable to ⁶⁸Ga-labeled FAPI-04. FAPI-74 based target volume dimensions were significantly increased compared to CT based planing and could impact treatment decisions in the future.