[18F]F-FAPI-42 PET dynamic imaging characteristics and multiparametric quantification of lung cancer: an exploratory study using uEXPLORER PET/CT

Abstract

Purpose

To explore the dynamic and parametric characteristics of [¹⁸F]F-FAPI-42 PET/CT in lung cancers.

Methods

Nineteen participants with newly diagnosed lung cancer underwent 60-min dynamic [¹⁸F]F-FAPI-42 PET/CT. Time-activity curves (TAC) were generated for tumors and normal organs, with kinetic parameters (K₁, K₂, K₃, K₄, K_i) calculated. A new parameter, the K ratio (K₁ + K₃)/(K₂ + K₄), was introduced to measure net uptake efficiency.

Results

In primary tumor (PT), [¹⁸F]F-FAPI-42 uptake showed a gradual increase followed by a plateau, contrasting with organs like the thyroid and pancreas, which showed rapid uptake and continuous washout. Compared to non-small cell lung cancer (NSCLC), small cell lung cancer (SCLC) lesions reached the plateau earlier (11 min vs. 14 min) but had a lower uptake. During the plateau phase, [¹⁸F]F-FAPI-42 demonstrated slight washout in SCLC, whereas its uptake increased slightly in NSCLC. Lymph node and distant metastases exhibited similar TAC profiles to primary tumors. Kinetic modeling revealed that an irreversible two-compartment model (irre-2TCM) best represented the pharmacokinetics of [¹⁸F]F-FAPI-42 in lung cancer, whereas re-2TCM was better suited for the pancreas and thyroid. Lower K₁, K₂, K₃ and K₄ were observed in PT compared to those in the pancreas and thyroid (P < 0.05), however, the K ratio in PT was found to be 2–3 times higher. SCLC had lower K_i and SUVmean than NSCLC (P < 0.05). Kinetic parameter differences were also observed between PT and metastatic lesions. Larger metastatic lymph nodes exhibited higher K₁, K_i, and K ratio than smaller ones.

Conclusion

Lung cancers exhibit distinct [¹⁸F]F-FAPI-42 dynamic and kinetic characteristics compared to the thyroid gland and pancreas. Differences were also observed between SCLC and NSCLC, primary and metastatic lesions, as well as larger versus smaller lesions. These findings provide valuable insights into the in vivo pharmacokinetics of [¹⁸F]F-FAPI-42, potentially improving the diagnosis of lung cancer.

Trial registration

ChiCTR2100045757. Registered April 24, 2021 retrospectively registered, http//www.chictr.org.cn.