FAPI PET-guided tumor volume delineation for radiotherapy planning: A comprehensive review across solid tumors

Area of Science:

• Oncology
• Radiotherapy
• Medical Imaging

Background:

• Accurate gross tumor volume (GTV) delineation is crucial for radiotherapy (RT) planning but is often limited by conventional imaging and [¹⁸F]FDG PET/CT.
• These conventional methods suffer from poor tumor-to-background contrast and non-specific inflammatory uptake, impacting precision.

Purpose of the Study:

• To review the current evidence on fibroblast activation protein inhibitor (FAPI) PET for GTV delineation across various solid tumors.
• To evaluate FAPI PET's potential to enhance GTV delineation, staging accuracy, and reduce interobserver variability compared to existing imaging modalities.

Main Methods:

• Systematic review of studies investigating FAPI PET in solid tumors for RT planning.
• Comparison of FAPI PET findings with conventional imaging ([¹⁸F]FDG PET/CT) and histopathological data where available.

Main Results:

• FAPI PET targets cancer-associated fibroblasts (CAFs) in the tumor microenvironment, offering a distinct biological target.
• FAPI PET frequently altered target volumes and RT planning in the reviewed studies.
• Evidence is limited by small, retrospective studies lacking histopathological validation and long-term outcome data.

Conclusions:

• FAPI PET is a promising complementary imaging tool for GTV delineation in selected clinical settings.
• Standardized segmentation methods and prospective multicenter studies are required.
• Further research is needed to determine if improved delineation with FAPI PET translates to better patient outcomes.