Prognostic value of tumor volume assessment on PSMA PET after 177Lu-PSMA radioligand therapy evaluated by PSMA PET/CT consensus statement and RECIP 1.0.

Introduction: Quantitative evaluation of prostate-specific membrane antigen (PSMA)- targeting positron emission tomography/computer tomography (PSMA PET/CT) remains challenging but is urgently needed for the use of standardized PET-based response criteria, such as the PSMA PET/CT consensus statement or RECIP 1. 0. A recent study evaluated the prognostic value of whole-body tumor volume using a semiautomatical method relying on a 50% threshold of maximum lesion standardized uptake value (PSMATV50). In the present study, we analyzed the suitability of this approach comparing 18F-PSMA-1007 to 68Ga-PSMA-11 PET/CT scans and the potential of PSMATV50 for the prediction of overall survival (OS) in patients before 177Lu-PSMA-radioligand therapy (PSMA RLT). Moreover, PSMATV50 was integrated into the PSMA PET/CT consensus statement as well as RECIP 1.0 and the prognostic value of these response classification systems was compared. Methods: This retrospective study included 70 patients with metastatic castration-resistant prostate cancer undergoing PSMA RLT. 33 patients were monitored by 68Ga-PSMA-11 PET/CT and 37 patients by 18F-PSMA-1007 PET/CT. PET/CT scans before (baseline) and at the end of PSMA RLT after 2-4 cycles (follow-up) were separately analyzed by two readers. PSMATV50 at baseline and its change to follow-up (ΔPSMATV50; expressed as a ratio) were correlated with OS using Cox proportional hazard regression. The results of both subgroups were compared. The integration of ΔPSMATV50 in existing response classification systems was evaluated. To assess and compare the discriminatory strength of these classification systems, Gönen & Heller concordance probability estimates (CPE) were calculated. Results: PSMATV50-determination was technically feasible in all examinations. A higher PSMATV50 at baseline and a higher ΔPSMATV50 were strongly associated with a shorter OS for both 68Ga-PSMA-11 (PSMATV50: HR 1.29 [1.05 - 1.55], p=0.009; ΔPSMATV50: HR 1.83 [1.08 - 3.09], p=0.024) and 18F-PSMA-1007 (PSMATV50: HR 1.84 [1.13 - 2.99], p=0.014; ΔPSMATV50: HR 1.23 [1.04 - 1.51], p=0.03). Response assessment provided high discriminatory power for OS for the PSMA PET/CT consensus statement (CPE 0.73) as well as RECIP 1.0 (CPE 0.74). Conclusion: PSMATV50 and ΔPSMATV50 proved to be predictive of OS not only for 68Ga-PSMA-11 but also for 18F-PSMA-1007 PET/CT scans. Subsequent integration of ΔPSMATV50 into the PSMA PET/CT consensus statement and RECIP 1.0 provided equally high prognostic value for both classification systems.

Journal of nuclear medicine : official publication, Society of Nuclear Medicine. 2022 Oct 27 [Epub ahead of print]

Felix Kind, Ann-Christin Eder, Cordula Annette Jilg, Philipp Hartrampf, Philipp T Meyer, Juri Ruf, Kerstin Michalski

Department of Nuclear Medicine, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germanyy, Germany., Department of Nuclear Medicine, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany., Department of Urology, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany., Department of Nuclear Medicine, University Hospital Wuerzburg, Wuerzburg, Germany.

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