Lesion Detection and Interobserver Agreement with Advanced Image Reconstruction for ¹⁸F-DCFPyL PET/CT in Patients with Biochemically Recurrent Prostate Cancer

Biochemically recurrent prostate cancer (BCR) is the main indication to perform prostate-specific membrane antigen positron emission tomography/computed tomography (PSMA PET/CT). However, localizing a BCR with PSMA PET/CT remains challenging in patients with low prostate-specific antigen (PSA) values. Here, we studied the impact of advanced PET image-reconstruction methods on BCR localization and interobserver agreement with 18F-DCFPyL PET/CT scans in patients with BCR and low PSA values. Methods: Twenty-four patients with BCR and a PSA <2.0 ng/ml were included. PET images were reconstructed with 4mm voxels and 2mm voxels, both with and without point-spread-functions (PSF). All scans were interpreted by four nuclear medicine physicians. Additionally, PET examinations of five patients with primary prostate cancer and confirmed absence of lymph node metastases (following lymph node dissection) were included, to assess the risk of introducing false-positive findings when using advanced reconstructions. BCR localization rates (scan positivity) were calculated based on consensus among our readers (≥three readers regarding a scan positive for BCR), as well as the individual scan interpretations of the readers. Results: In the consensus analysis, BCR localization rates were not higher using advanced reconstruction methods (62.5-66.7%) compared to the 4mm reconstruction (62.5%). Based on individual readings, however, more scans were positive using the 2mm (74.0%, 95% CI 65.0-82.9%)(P = 0.027) and 2mm+PSF reconstruction (75.0%, 95% CI 66.2-83.8%)(P = 0.014) compared to the 4mm reconstruction (65.6%, 95% CI 56.0-75.3%). A higher number of lesions was detected on the 2mm (median 2 lesions, interquartile range 1-3) compared to 4mm scans (median 1, interquartile range 0-3; P = 0.008). The advanced reconstructions methods did not increase interobserver agreement (80.6-84.7%), compared to the 4mm scans (75.7%, P = 0.08-0.25). In the patients with primary PCa, an equal number of false-positive lesions was observed among the different reconstruction methods (overall n = 13). Conclusion: Applying advanced image-reconstructions for 18F-DCFPyL PET/CT scans did not increase BCR localization in patients with BCR and low PSA values (reader consensus). Yet, the increased number of positive individual readings may imply that further development of image-reconstruction methods holds potential to improve BCR localization. No improved interobserver agreement was observed with advanced reconstruction compared to standard 4mm reconstructions.