FAPI-PET imaging and biodistribution analysis

All patients gave written informed consent for undergoing ⁶⁸Ga-FAPI PET-CT. The radiopharmaceutical was administered intravenously (80 nmol/GBq) followed by image acquisition 30 min after tracer administration. The PET/CT scans were performed with a Biograph mCT Flow PET/CT-Scanner (Siemens Medical Solutions). A low-dose whole body CT scan (130 keV, 30 mAs, CareDose; reconstructed with a soft-tissue kernel to a slice thickness of 5 mm) was used for attenuation correction and image fusion. A 3-D emission scan (matrix 200 × 200) was performed, subsequently using FlowMotion (Siemens). The emission data was corrected for randoms, scatter and decay. Reconstruction was performed with an ordered subset expectation maximisation (OSEM) algorithm with two iterations/21 subsets and Gauss-filtered to a transaxial resolution of 5 mm at full width at half maximum (FWHM).

Circular volumes of interest were used inside tumour lesions and healthy tissues to quantify the radiotracer biodistribution in patients. This resulted in SUV_max and SUV_mean.