ESTRO 2025 - Abstract Book

S2085

Clinical - Urology

ESTRO 2025

3984

Proffered Paper Impact of staging PSMA-PET/CT on radiotherapy planning in men with high-risk prostate cancer – results of a prospective multicenter randomized trial Stefan A Koerber 1,2 , Christoph A Grott 2 , Irene Burger 3 , Ken Herrmann 4 , Joerg Kotzerke 5 , Christian La Fougère 6 , Philipp Meyer 7 , Irene Virgolini 8 , Wolfgang Weber 9 , Klaus Kopka 10 , Uwe Haberkorn 11 , Juergen Debus 2 , Matthias Eiber 9 , Frederik L Giesel 12,11 1 Department of Radiation Oncology, Barmherzige Brueder Hospital Regensburg, Regensburg, Germany. 2 Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg, Germany. 3 Department of Nuclear Medicine, University Hospital Zurich, Zurich, Switzerland. 4 Department of Nuclear Medicine, University Hospital Essen, Essen, Germany. 5 Department of Nuclear Medicine, University Hospital Dresden, Dresden, Germany. 6 Department of Nuclear Medicine, University Hospital Tuebingen, Tuebingen, Germany. 7 Department of Nuclear Medicine, University Hospital Freiburg, Freiburg, Germany. 8 Department of Nuclear Medicine, University Hospital Innsbruck, Innsbruck, Austria. 9 Department of Nuclear Medicine, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany. 10 Institute of Radiopharmaceutical Cancer Research, Helmholtz-Zentrum Dresden Rossendorf (HZDR), Dresden, Germany. 11 Department of Nuclear Medicine, Heidelberg University Hospital, Heidelberg, Germany. 12 Department of Nuclear Medicine, University Hospital Duesseldorf, Duesseldorf, Germany Purpose/Objective: The German Cancer Consortium (DKTK) prospective multicenter phase 1/2 trial investigated the safety and diagnostic accuracy of PET imaging targeting the Prostate Specific Membrane Antigen (PSMA) for treatment-naïve patients with prostate cancer using [ 68 Ga]Ga-PSMA-11. As a secondary outcome, the impact on radiation oncology and target volume delineation as assessed and is reported here. Material/Methods: In this international, prospective multicenter trial (EudraCT 2016-001815-19), patients with high-risk prostate cancer were recruited in 9 urooncological sites in Germany, Austria and Switzerland. Image interpretation of [ 68 Ga]Ga PSMA-11 PET/CT was performed by 3 independent and board-approved readers in a central reading process. For radiation therapy (RT) planning (treatment simulation), patients were randomised and assigned to either conventional imaging or [ 68 Ga]Ga-PSMA-11 PET imaging and crossed-over 4 weeks after randomisation. The accuracy of the initial therapy plan regarding treatment volume delineation was defined after correlation of both imaging modalities and access to histopathological data. Results: From 173 treatment-naïve patients with prostate cancer undergoing PSMA-PET imaging with [ 68 Ga]Ga-PSMA-11, 139 men were included for the RT study. In total, 556 target volumes according to RTOG guidelines and RT plans (conventional imaging vs. PSMA-PET imaging +/- prophylactic pelvic nodes for each arm) were created. PSMA-PET guided target volume delineation resulted in modifications in 29 out of 139 patients (20.9%). For 23 patients, major changes of the RT plan occurred. This included upstaging to N1-disease, nodes outside the international target volume recommendations and downstaging of morphological suspicious findings. However, there was a lack of the detection of small nodal lesions (< 5mm) in [ 68 Ga]Ga-PSMA-11 PET/CT leading to potential undertreatment of high risk patients undergoing definitive radiation therapy without elective nodal irradiation. Conclusion: Our findings obtained from a prospective randomized trial confirmed the necessary role of primary staging with [ 68 Ga]Ga-PSMA-11 PET/CT for treatment-naïve patients with high-risk prostate carcinoma. The use of [ 68 Ga]Ga PSMA-11 for staging, results in significant changes in radiooncological management. Nevertheless, the role of elective nodal irradiation should individually be discussed at the presence of high risk-factors also when staging with [ 68 Ga]Ga-PSMA-11 PET is negative for nodal disease.

Keywords: prostate cancer, PSMA-PET/CT, primary staging