Evaluation of 68Ga-PSMA I&T PET/CT in 240 Patients with Biochemical Relapse After Primary Therapy for Prostate Cancer : Intraindividual Comparison between Standard and Delayed Imaging

Objectives: ⁶⁸Ga-Labelled prostate-specific membrane antigen (PSMA) ligands have gained increased interest as highly sensitive imaging agents for evaluation of biochemical recurrence in patients after primary therapy for prostate cancer. Delayed imaging has been suggested to improve lesion-to-background ratios using other radiotracers. In this study, we sought to determine the value of additional delayed abdominal imaging inPET/CT for detection of biochemically recurrent prostate cancer, using the ligand ⁶⁸Ga-PSMA I&T.

Methods: The study population consisted of 240 men (69.8±7.5 years; range, 46.4-89.8 years) who were referred for a ⁶⁸Ga-PSMA I&T PET/CT for detection of biochemical recurrence after primary therapy for prostate cancer. Imaging consisted of a standard whole-body PET/CT (1h p.i.), followed by delayed (3h p.i.) imaging of the abdomen. PSA-stratified proportions of positive PET/CT results, standardized uptake values and lesion-to-background ratios were analyzed, and compared between standard and delayed imaging.

Results: The overall detection efficacy of ⁶⁸Ga-PSMA I&T PET/CT was 94.2%, 71.8%, 58.6% and 50.0% for PSA levels of 蠅2, 1 to <2, 0.5 to <1, and 0.01 to <0.5 ng/mL, respectively. Although the target-to-lesion ratio improved significantly over time (P<0.0001), the majority (1096 of 1134 lesions; 96.6%) of all lesions suggestive of recurrent disease could already be detected in standard imaging. Delayed imaging at 3h p.i. exclusively identified pathologic findings in 5.4% (10/184) of abnormal ⁶⁸Ga-PSMA I&T PET/CT scans, and exclusively detected 38 of 1134 (3.4%) of all lesions suggestive of recurrent disease. The intensity of ⁶⁸Ga-PSMA I&T accumulation was significantly higher in patients receiving ADT (P&#8804;0.004), but not significantly higher in patients with higher Gleason scores (P蠅0.07)

Conclusion: ⁶⁸GaPSMA I&T PET/CT shows high detection rates in patients with biochemical relapse after primary therapy for prostate cancer. Delayed imaging can detect lesions with improved contrast compared to standard imaging. However, the impact on detection efficacy is limited. Standard imaging at 1 h p.i. is sufficient when using the ligand ⁶⁸GaPSMA I&T. Research Support: None

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