Abstract

Tobias Hölscher¹, Michael Baumann², Jörg Kotzerke³, Manfred Wirth⁴, Christian Thomas⁴, Daniel Zips⁵, Steffen Löck⁶, Mechthild Krause^7,9,10, Fabian Lohaus⁸

¹Department of Radiotherapy and Radiation Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany; ²_, German Cancer Research Center (DKFZ), Heidelberg, Germany; ³Department of Nuclearmedicine, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden , Dresden, Germany; ⁴Department of Urology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden , Dresden, Germany; ⁵Department of Radiation Oncology, Universität Tübingen, Tübingen, Germany; ⁶OncoRay – National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Helmholtz-Zentrum Dresden - Rossendorf, Dresden, Germany; ⁷Department of Radiotherapy and Radiation Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden , Dresden, Germany; ⁸Department of Radiotherapy and Radiation Oncology,, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany; ⁹National Center for Tumor Diseases (NCT), Partner Site Dresden, Germany: German Cancer Research Center (DKFZ), Heidelberg, Germany, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany, and; Helmholtz Association / Helmholtz-Zentrum Dresden – Rossendorf (HZDR), Dresden, Germany; ¹⁰German Cancer Consortium (DKTK), Partner Site Dresden, German Cancer Research Center (DKFZ), Heidelberg, Germany

PSA-progression after curative primary therapy is common in patients with prostate cancer. Modern imaging methods, like PSMA-PET hybrid imaging, may detect patients with oligometastastic disease at low PSA-levels. Metastases-directed local ablative radiotherapy (aRT) is a safe option in this situation. Local control and the pattern of progression is evaluated for this prospective clinical phase II trial.

At two German centers, patients with PSA progression after local curative treatment had PSMA-PET-CT imaging. Patients with up to four PSMA-PET positive metastases (MET) were included in the clinical trial. Patients had no ongoing androgen deprivation therapy (ADT), a PSA <10 ng/ml and no severe comorbidity. The patients were treated with 3 x 10 Gy (SABR) or 25 x 2.0 Gy to all PSMA-PET positive MET (involved lesions). The primary endpoint was toxicity within two years after aRT. Here we report secondary endpoints including the pattern of progression and local control after aRT.

Between 2014 and 2018, 63 patients had aRT of 89 MET (68 lymph node (ln-) MET and 21 bone (OSS-) MET). The mean volumes of GTV and PTV were 2.2 ml and 15 ml. The 50 Gy scheme was used in 34 MET and 55 MET were treated with SABR. The median follow-up time was 36.6 months.

Local progression occurred in 7 MET, resulting in a local control of >90 % after 3 years. Patients with OSS MET and with a larger (than mean) PTV were at higher risk of local progression (log-rank test: p < 0,001 and p = 0,01, respectively, see figure). Regional progression adjacent to the irradiated area was observed in 16 of 46 patients with at least one Ln-MET (51% free of regional progression @3y). In 34 patients (54%), a distant progression was reported. Median time to detection of other progressive lesions was 24 months. 13 patients (21%) had another aRT.

Local ablative radiotherapy in patients with PSMA-PET staged oligometastatic prostate cancer can achieve high rates of local control, but regional or distant progression is common. Further studies are warranted, e.g. to define optimal target volume coverage.