Early image acquisition ⁶⁸Ga-FAPI-46-PET/CT in prone position is promising in the workup of rectosigmoid and anal carcinoma.

Abstract

To overcome difficulties with regard to anatomic discrimination of intrapelvic tumors and non-specific intrapelvic uptake (i.e. excreted activity in the urinary bladder) by early acquisition of FAPI-PET in prone position. 15 patients with rectosigmoid (RSC) and squamous cell carcinoma of the anus (SCCA) underwent early-imaging ⁶⁸Ga-FAPI-46-PET/CT-scans in prone position 5.9 ± 1.3 min after radiotracer injection. SUV and metric values for primary tumors, metastases, bladder and background tissues were measured. Tumor-to-background ratios (TBR) were calculated. Despite early acquisition, SUV was already high in tumors and metastases, leading to high TBR. A sufficient, on average at least 2.56 ± 0.66 cm, spatial distance between tumor and bladder uptake was observed in all cases. An early-imaging protocol in prone position with ⁶⁸Ga-FAPI-46-PET/CT presents a viable option for non-invasive staging of SCCA and RSC with high TBR and good spatial separation from the urinary bladder.