Evaluation of [68 Ga]Ga-PSMA-I&T PET/CT with additional late scans of the pelvis in prostate-specific antigen recurrence using the PROMISE criteria

BACKGROUND: PSMA PET/CT is the recommended imaging test in cases with prostate-specific antigen (PSA) recurrence after primary therapy of prostate cancer (PCa). However, imaging protocols remain a topic of active research. The aim of the presented study was to examine the impact of additional late scans of the pelvis in [68 Ga]Ga-PSMA-I&T PET/CT of patients with rising PSA after prostatectomy.

METHODS: A total of 297 patients (median PSA 0.35 ng/ml, interquartile range (IQR) 0.2-0.8) who underwent early whole-body [68 Ga]Ga-PSMA-I&T PET/CT (median dose 141 MBq, IQR 120-163; median 86 min, IQR 56-107) and additional late scans of the pelvis (median 180 min, IQR 170-191) were investigated retrospectively. Early and late images were staged separately according to the PROMISE criteria and compared with a final consensus of both. Standardized uptake values were analyzed for early and late scans.

RESULTS: One hundred and thirty-four (45.1%) [68 Ga]Ga-PSMA-I&T PET/CT showed evidence of recurrent PCa (114/38.4% early, 131/44.1% late). Of 195 lesions, 144 (73.8%) were identified correctly on early scans. 191 (97.9%) lesions were detected on late imaging. The lesion SUVmax (median 3.4, IQR 0.4-6.5 vs. median 3.9, IQR 2.6-8.2) as well as the SUVmax to background ratio (median 9.4, IQR 1.7-19.1 vs. median 15.5, IQR 9.6-34.1) increased significantly between the imaging time points (p < 0.01, respectively). Compared to the final consensus, the miTNM-staging of early scans changed in 58 (19.5%) cases. Of these, 31 patients (10.4%) with negative early scans (T0 N0 M0) were upstaged. Twenty-seven (9.1%) patients with PCa characteristic lesions on early imaging (> T0 N0 M0) were up- and/or downstaged. In 4 (1.3%) cases, PCa-related lesions were only detectable on early PET/CT leading to upstagings of late imaging.

CONCLUSIONS: Additional late scans of the pelvis in [68 Ga]Ga-PSMA-I&T PET/CT detected more lesions and an increasing contrast compared to early imaging. This influenced the final miTNM-staging substantially.