Sep 29

SS 29 - Intensify, Shorten, or Personalize? Modern Approaches to Post-prostatectomy RT

LBA 13 - Phase II Results of the Randomized StereoBed Trial: Salvage Stereotactic Body Radiotherapy to the Prostate Bed for Biochemical Recurrence after Radical Prostatectomy

01:10pm - 01:20pm ET

Room 210

Presenter(s)

Pauline De Bruyn, MD - Institut Jules Bordet- Université Libre de Bruxelles, Department of Radiation-Oncology, Etterbeek, Brussels-C

P. De Bruyn¹, N. Jullian¹, P. Dirix², C. Draulans³, P. Nguyen⁴, P. Bulens⁵, N. Sundahl⁶, S. Palumbo⁷, S. Meersschout⁸, A. Vandermeulen⁹, B. Engels¹⁰, L. Vandenbergh¹¹, C. Berghen¹², B. Vanneste¹³, P. Ost², R. Van den Begin¹, and P. Kristanto¹⁴; ¹Department of Radiation Oncology, Institut Jules Bordet, Brussels, Belgium, ²Department of Radiation Oncology, Iridium Network, Antwerp, Belgium, ³Department of Radiation Oncology, AZ Sint-Maarten, Mechelen, Belgium, ⁴Department of Radiotherapy, CHU UCL Namur - Site Saint Elisabeth, Namur, Belgium, ⁵Department of Radiation Oncology, Limburgs Oncologisch Centrum, Hasselt, Belgium, ⁶Department of Radiation Oncology, AZ Groeninge, Kortrijk, Belgium, ⁷Department of Radiation Oncology, Centres Hospitaliers Universitaires HELORA, La Louvière, Belgium, ⁸Department of Radiation Oncology, AZ Sint-Jan, Bruges, Belgium, ⁹Department of Radiation Oncology, Cliniques Universitaires Saint-Luc, Brussels, Belgium, ¹⁰Department of Radiation Oncology, AZORG, Aalst, Belgium, ¹¹Department of Radiation Oncology, Limburgs Oncologisch Centrum, Genk, Belgium, ¹²Department of Radiation Oncology, University Hospitals Leuven, Leuven, Belgium, ¹³Department of Radiation Oncology, Ghent University Hospital, Ghent, Belgium, ¹⁴Hôpital Universitaire de Bruxelles (H.U.B), Brussels, -1, Belgium

Purpose/Objective(s):

Salvage radiotherapy (RT) is a well-established standard-of-care treatment for biochemical recurrence (BCR) after radical prostatectomy. Stereotactic body radiotherapy (SBRT) may offer a shorter treatment duration and favorable radiobiological characteristics, but evidence in the postoperative setting remains limited. We report phase II interim patient-reported outcomes (PROs) and toxicity from StereoBed.

Materials/Methods:

StereoBed (NCT06523634) is a multicenter randomized seamless phase II/III non-inferiority trial. Patients with persistent or rising PSA after prostatectomy are randomized 1:1 to prostate bed RT with either conventionally/moderately fractionated RT (64–70 Gy in 32–35 fractions or 52.5 Gy in 20 fractions) or SBRT (32 Gy in 5 fractions). Randomization has been stratified by the administration of androgen-deprivation therapy (ADT), whole pelvis radiotherapy (WPRT) and by the study centers. The primary objective is to demonstrate that SBRT does not increase patient-reported urinary (GU) and bowel (GI) symptoms compared to standard-of-care (SOC) fractionation evaluated by 2-year changes from baseline in EPIC-26 GU and GI domain scores. At the end of phase III, 207 evaluable patients are required. A pre-specified phase II interim futility analysis was performed after 62 evaluable patients using 6-month EPIC-26 scores.

We are reporting the phase II results, including 6-month PROMs and CTCAE 5.0 grade =2 GU/GI toxicity.

Results:

Among the 62 patients analysed, 30 (48.4%) received salvage RT alone, 23 (37.1%) received whole-pelvis RT with ADT, and 9 (14.5%) received ADT without whole-pelvis RT.

The baseline median EPIC-GU score was 86.8 (IQR: 73.0, 100.0) in the control arm and 91.7 (IQR: 80.0, 100.0) in the experimental arm. The median change in EPIC-GU score at 6 months from baseline was -4.1 (IQR: -11.4, 0.0) in the control arm and 0.0 (IQR: -3.1, 6.3) in the experimental arm. The baseline median EPIC-GI score was 100.0 (IQR: 95.8, 100.0) in the control arm and 100.0 (IQR: 100.0, 100.0) in the experimental arm. The median change in EPIC-GI score at 6 months from baseline was 0.0 (IQR: -4.2, 0.0) in the control arm and 0.0 (IQR: -8.3, 0.0) in the experimental arm. For both EPIC-GU and EPIC-GI change scores, there was no significant difference between arms and the futility boundary was not crossed. No significant difference in treatment-related adverse events was observed between the two arms. Grade = 2 GU events were reported in 9.7% of patients in the control arm versus 3.2% in the experimental arm. Grade = 2 GI events occurred in 16.1% and 19.4% of patients, respectively, with a single grade 3 GI event recorded in the control arm.

Conclusion:

This planned phase II interim analysis demonstrates that salvage SBRT is safe and well tolerated, with low rates of grade = 2 toxicity and no grade 3 GU events up to 6 months after RT. Futility boundaries were not crossed for either EPIC-GU or EPIC-GI endpoints, supporting trial continuation.