Abstract

Background: This study aimed to determine whether incorporating radiologic contrast during the excretory (urographic) phase enhances the detection of recurrence on [68Ga]Ga-PSMA-11 PET/CT in patients with biochemical relapse (BCR) following radical prostatectomy (RP). Methods: A single-center retrospective analysis included 43 men with BCR after RP who underwent [68Ga]Ga-PSMA-11 PET/CT. Each patient underwent two comparative assessments. In the first assessment, whole-body PET images acquired at 60 min post-injection were fused with the non-contrast CT from early dynamic pelvic imaging (PET/CTd), and local recurrence and pelvic nodal involvement were evaluated according to PROMISE V2 and E-PSMA frameworks by two blinded readers. In the second assessment, the same PET dataset was fused with the excretory-phase CT urography (CT-U) obtained during the same imaging session at 60 min post-injection, and the same parameters were re-evaluated. Endpoints included surgical-bed classification, peri-ureteric nodal status, reader confidence, ureter visualization/opacification, and interpretation time. Inter- and intra-observer agreement was assessed, and discrepancies were resolved by consensus. Results: Surgical-bed positivity decreased from 12/43 (27.9%) on PET/CTd to 5/43 (11.6%) on PET/CT-U, leading to reclassification in seven patients (p = 0.016). Reader confidence improved significantly in five cases (p < 0.005). Peri-ureteric nodal status was changed in four patients (two positive-to-negative and two negative-to-positive), with overall positivity unchanged (5/43 vs. 5/43; p = 1.000). Ureter visualization improved markedly (inadequate: 31 vs. 10 cases), reducing diagnostic uncertainty by 50%. CT-U opacification was ≥50% in most cases (κ = 0.814), enabling reliable delineation of the ureteral course. Inter-reader agreement remained strong (surgical bed κ: 0.944 vs. 0.876; nodes κ: 0.896 both). Interpretation time decreased for both readers (senior: 3.12 vs. 2.10 min (−32.7%); junior: 4.06 vs. 2.42 min (−40.4%)). Conclusions: Adding an excretory-phase CT urography to [68Ga]Ga-PSMA-11 PET/CT improves diagnostic confidence, reduces interpretive uncertainty in the surgical bed, clarifies peri-ureteric nodal findings, enhances ureter visualization, and shortens interpretation time. CT-U is a practical enhancement to low-dose PET/CT protocols for BCR after RP.

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