Analysis of perfusion parameters in low-level PSA recurrence of prostate cancer after radical prostatectomy prior to salvage therapy in a combined imaging protocol of whole-body PSMA-PET/CT and pelvic PET/mpMR

Introduction: Multiparametric MRI (mpMR) including dynamic-contrast-enhanced MR (DCE-MR) is promising for detecting local recurrence in prostate cancer (PCa) patients with biochemical relapse. We analyzed its value in low-level PSA-relapse after radical prostatectomy (RP), prior to salvage therapy (ST) in a combined approach using PSMA-PET/CT and PSMA-PET/mpMR imaging with a focus on perfusion parameters.

Methods: 28 patients (age 65±8; GS 7-9) with low-level PSA relapse (median (range) 0.24 (0.07-0.61) ng/ml) and positive local PCa findings in PET/mpMR, without salvage therapy or androgen deprivation therapy (ADT) after RP were examined with whole-body PET/CT- followed by pelvic PET/mpMR imaging (90 minutes p.i. of 309±48 MBq [18F]siPSMA-14 in 25/28 patients without furosemide or 60 minutes p.i. of 179±11 MBq of [68Ga] PSMA-11 in 3/28 patients with furosemide). In all patients local lesions were evaluated using perfusion parameters (Ktrans, iAUC) and tracer uptake (SUVmean/max values) in comparison to muscle as reference. Statistic measurements were performed using Mann Whitney U test and Spearman rank correlation. PSA time course after ST in patients without ADT was used for Follow-up as best valuable comparator.

Results: In all patients (100% (28/28)) suspicious lesions showed contrast enhancement in DCE-MR, in 89% (25/28) with corresponding PSMA-expression. Lesions were predominantly localized at the perianastomotic site in 64% (18/28), in the former seminal vesicle region in 14% (4/28), in the former rectoprostatic angle in 11% (3/28), in the retrovesical region in 7% (2/28) and in the former prostate bed in one case (4% (1/28)). Perfusion analysis of the lesions (volume: 65±5 mm³) resulted in significantly higher Ktrans, iAUC and SUVmean/max values (each p=<0.05) with Ktrans: 0.30±0.11 (reference: 0.03±0.01), iAUC: 0.32±0.01 (reference: 0.04±0.01) and SUVmean/max median (range): 3.0 (1.9-21.0) / 4.9 (2.6-38.2) compared to reference 0.4 (0.3-0.6) / 0.7 (0.4-0.9). A positive significant correlation of Ktrans to iAUC values was measured, whereas SUV values showed no correlation to Ktrans, iAUC and volume. In 32% (9/28) of patients after ST PSA follow-up was available. In this subgroup a PSA response to ST of 75% ± 20% was documented.

Conclusions: PSMA-PET/mpMR enables characterization of perfusion patterns of small lesions suspicious for local PCa recurrences after RP. In most cases elevated PSMA-expression was noted, however there was no correlation with perfusion parameters, suggesting synergistic information with respect to molecular tissue characterization. A sufficient PSA-response in a subgroup of patients with follow-up after PET/mpMR guided treatment suggests that combined imaging of whole-body PSMA-PET/CT followed by pelvic PET/mpMR may help with patient selection prior to salvage therapy. Thus, precise local tumor detection for target-directed treatments, e.g. radiotherapy or radioguided surgery, can be achieved.

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