Original Article
Utilization of 68Ga-FAPI PET/CT improves the gross tumor volume delineation in nasopharyngeal carcinoma within a safe radiation dose to organs at risk
Abstract
Background: Accurate delineation of the nasopharynx gross tumor volume (GTVnx) of nasopharyngeal carcinoma (NPC) is crucial for patients requiring radiotherapy, as it correlates with prognosis. Current GTVnx delineation methods have significant shortcomings, often resulting in insufficient coverage of the radiotherapy target area. Gallium-68-labeled fibroblast activation protein inhibitor (68Ga-FAPI) is an emerging and promising tumor imaging agent. This study aims to evaluate the effectiveness of combining 68Ga-FAPI positron emission tomography/computed tomography (PET/CT) for delineating GTVnx in NPC.
Methods: This prospective study enrolled 19 patients with NPC who underwent 68Ga-FAPI PET/CT from August 2022 to August 2023. GTVnx were delineated, quantified, and compared based on enhanced magnetic resonance imaging (MRI),68Ga-FAPI PET/CT, and the fusion of both imaging modalities, and were respectively named and abbreviated as GTVnx-MRI, GTVnx-FAPI, and GTVnx-MRI + FAPI. GTVnx-FAPI was automatically delineated using maximum standardized uptake value (SUVmax) thresholds, with the optimal threshold determined by the Jaccard index and intraclass correlation coefficient (ICC). Radiotherapy plans were developed based on GTVnx-MRI and GTVnx-MRI + FAPI to assess radiation doses to organs at risk (OARs). A paired t-test was employed to compare variables among groups.
Results: Nineteen pathologically confirmed NPC patients [mean age, 48.84±12.12 years (range, 24–70 years); 12 men (63.16%)] were enrolled. All included NPC patients demonstrated high 68Ga-FAPI uptake in their primary tumor lesions. The 20% SUVmax on 68Ga-FAPI PET/CT of the primary tumor (GTVnx-FAPI20%) was determined to be the most suitable threshold for guiding GTVnx-FAPI with an ICC of 0.891. The GTVnx-MRI + FAPI20% was significant lager than both GTVnx-MRI and GTVnx-FAPI20%, with average measurements of 24.93±17.31, 17.44±13.12, and 16.29±11.15 cm3, respectively(P<0.001). In the radiotherapy plan based on GTVnx-MRI + FAPI20%,radiation dose to all OARs was not increased significantly compared to that based on GTVnx-MRI.
Conclusions: The combined use of 68Ga-FAPI PET/CT shows potential to enhance the delineation of GTVnx in NPC patients while maintaining OAR doses within acceptable limits.
Chinese Clinical Trial Registry under the registration number: ChiCTR2300074538.
