Improved Accuracy and Reliability of PRIMARY Scoring Using Delayed [⁶⁸Ga] Ga-PSMA PET/CT Imaging

Area of Science:

• Nuclear Medicine
• Radiology
• Uro-oncology

Background:

• Prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) is crucial for prostate cancer staging.
• Standard imaging protocols involve uptake assessments at early time points.
• Delayed imaging may offer improved lesion characterization by reducing background activity and enhancing tumor-to-background ratios.

Purpose of the Study:

• To evaluate the efficacy of PRIMARY scoring using [⁶⁸Ga]Ga-PSMA PET/CT at standard versus delayed time points.
• To assess the added value of delayed imaging in improving PRIMARY scoring for prostate cancer detection.

Main Methods:

• 140 patients with International Society of Urological Pathology (ISUP) grade groups 1-2 underwent standard (median 60 min) and delayed (median 138 min) [⁶⁸Ga]Ga-PSMA PET/CT before radical prostatectomy.
• Images were reviewed by nuclear medicine physicians for PRIMARY scoring, with intra- and inter-observer agreement analyses.

Main Results:

• Delayed imaging significantly shifted PRIMARY scores towards higher values (90% vs 71% for scores 3-5).
• Sensitivity for clinically significant prostate cancer (csPCa) increased from 71% to 92% with delayed PRIMARY scoring.
• Inter- and intra-observer agreement improved with delayed imaging (Fleiss kappa 0.61-0.72 vs 0.47-0.52).

Conclusions:

• Delayed [⁶⁸Ga]Ga-PSMA PET/CT imaging enhances the differentiation between malignant and benign lesions.
• Delayed imaging improves the reliability and accuracy of PRIMARY scoring for detecting csPCa.
• The enhanced reliability of delayed imaging is supported by improved inter- and intra-observer agreement.