Is there a diagnostic benefit of late-phase abdomino-pelvic PET/CT after urination as part of whole-body (68) Ga-PSMA-11 PET/CT for restaging patients with biochemical recurrence of prostate cancer after radical prostatectomy?

BACKGROUND: To assess the diagnostic value of an additional late-phase PET/CT scan after urination as part of (68) Ga-PSMA-11 PET/CT for the restaging of patients with biochemically recurrent prostate cancer (BCR). METHODS: This retrospective trial included patients with BCR following radical prostatectomy, who underwent standard whole-body early-phase PET/CT performed 105 ± 45 min and an additional late-phase PET/CT performed 159 ± 13 min after injection of (68) Ga-PSMA-11. Late-phase PET/CT covered a body volume from below the liver to the upper thighs and was conducted after patients had used the bathroom to empty their urinary bladder. Early- and late-phase images were evaluated regarding lesion count, type, localisation, and SUVmax. Reference standard was histopathology and/or follow-up imaging. RESULTS: Whole-body early-phase PET/CT detected 93 prostate cancer lesions in 33 patients. Late-phase PET/CT detected two additional lesions in two patients, both local recurrences. In total, there were 57 nodal, 28 bone, and 3 lung metastases, and 7 local recurrences. Between early- and late-phase PET/CT, lymph node metastases showed a significant increase of SUVmax from 14.5 ± 11.6 to 21.5 ± 17.6 (p = 0.00007), translating to a factor of + 1.6. Benign lymph nodes in the respective regions showed a significantly lower increase of SUVmax of 1.4 ± 0.5 to 1.7 ± 0.5 (p = 0.0014, factor of + 1.2). Local recurrences and bone metastases had a SUVmax on late-phase PET/CT that was + 1.7 and + 1.1 times higher than the SUVmax on early-phase PET/CT, respectively. CONCLUSION: In patients with BCR following radical prostatectomy, an additional abdomino-pelvic late-phase (68) Ga-PSMA-11 PET/CT scan performed after emptying the urinary bladder may help to detect local recurrences missed on standard whole-body (68) Ga-PSMA-11 PET/CT. Lymph node metastases show a higher SUVmax and a stronger increase of SUVmax than benign lymph nodes on late-phase PET/CT, hence, biphasic (68) Ga-PSMA-11 PET/CT might help to distinguish between malignant and benign nodes. Bone metastases, and especially local recurrences, also demonstrate a metabolic increase over time.