3170 - Early Results from a Prospective Trial Testing Stereotactic Salvage Radiotherapy for Macroscopic Prostate Bed Recurrence after Prostatectomy-STARR(NCT05455736)

G. Francolini¹, V. Di Cataldo¹, P. Garlatti¹, M. Loi¹, D. Greto¹, G. Simontacchi², V. Salvestrini¹, L. Masi³, R. Doro⁴, and L. Livi⁵; ¹Radiation Oncology, Careggi University Hospital, University of Florence, Florence, Italy, ²Radiation Oncology, Careggi University Hospital, University of Florence, Firenze, Italy, ³Istituto Fiorentino di Cura e Assistenza (IFCA), CyberKnife Center, Florence, Italy, ⁴Istituto Fiorentino di Cura e Assistenza (IFCA), CyberKnife Center, Firenze, Italy, ⁵Department of Experimental Clinical and Biomedical Sciences “Mario Serio”, University of Florence, Florence, Italy

Purpose/Objective(s): Salvage radiotherapy (SRT) is one of the most widely used approaches in case of biochemical recurrence after radical prostatectomy for prostate cancer. Macroscopic recurrence within the prostate bed in this scenario is often detected through PSMA PET/CT or Magnetic resonance imaging (MRI). Stereotactic salvage radiotherapy (SSRT) has been proposed as a method to improve disease control by dose escalation in these patients. STARR is a prospective trial exploring clinical outcomes after SSRT on macroscopic recurrence within prostate bed after radical prostatectomy. Materials/

Methods: STARR trial is a prospective multicenter study enrolling subjects affected by prostate bed macroscopic recurrence. All relapses were detected by Choline, PSMA CT-PET or MRI performed after a post prostatectomy PSA rise above 0.2 ng/ml. All patients with regional or distant metastatic disease were excluded. SSRT consisting in a total dose of 35 Gy in 5 fractions every other day was administered on macroscopic relapse defined through CT-PET and/or MRI co-registration with planning CT. Androgen Deprivation therapy (ADT) was not prescribed. A PSA nadir <0.2 ng/ml and <50% of baseline, respectively, were defined as complete biochemical response (CBR) or biochemical response (BR).
Results: Sixty-one patients were enrolled between March 2021 and November 2023. The current analysis included 50 enrolled patients at the promoting institution with > 3 months of follow up. After a median follow up of 10 months (95%CI 7-17), Acute genitourinary and gastrointestinal toxicity occurred in 4 (3 G1 and 1 G2), and 5 patients (3 G1 and 2 G2), respectively. Late genitourinary and gastrointestinal toxicity were identified in 7 (all G1) and 1 patient (G2), respectively. BR and CBR were detected at 3 months in 41 (82%) and 23 (46%) cases, respectively. Seven recurrences were detected (3 biochemical and 4 metastatic recurrences detected through PSMA PET-CT) Forty-six patients (92%) were free from ADT at the end of follow up.
Conclusion: SSRT yielded optimal results in terms of safety, with only mild adverse events. Biochemical outcomes are promising, with a significant benefit in terms of clinically meaningful outcomes (i.e. new distant metastases occurrence and need for ADT start).