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For radiotherapy planning, 18F-FDG-PET/CT is commonly used for several tumors such as lung cancer. However, the tracer has been partially challenging due to physiological brown fat uptake, inflammation or low glucose transporter and hexokinase activity in certain tumor types. Since the introduction of PET imaging of the fibroblast activation protein (FAP), novel and promising FAP-specific tracers with high diagnostic performance were introduced. The current study evaluated the impact of 68Ga-FAPI-PET/CT on tumor stage and (radio)oncological management in a large cohort of patients with various cancers.

A total of 227 patients with 25 different kinds of cancer were included in this retrospective study. Most common tumor types were pancreatic (n = 78), head and neck (n = 29) and lung cancer (n = 23). Tracer uptake was quantified by standardized uptake values (SUV)max and (SUV)mean. After comparison with standard imaging, changes in tumor stage and (radio)oncological management were recorded.

After FAPI-imaging, a high tumor-to-background ratio of more than 3 in most lesions was observed due to a low background activity in normal tissue. For more than 50% of all patients, there was a change of TNM stage. Upstaging was more frequent than downstaging considering results from the novel imaging probe (55.6%). With regard to (radio)oncological management, a change occurred for 56.0% of all patients after 68Ga-FAPI-PET/CT. The most common reason was an improvement for target volume delineation, however, major changes (e.g. change of therapy modality) were observed for almost 15% of the group.

This large study with different kinds of cancer demonstrated promising results particularly among cancers less suitable for conventional PET imaging such as pancreatic cancer. Nevertheless, prospective trials including histopathological verification are mandatorily required to confirm the increasing importance of 68Ga-FAPI-PET/CT and finally assess the impact on radiation oncology.