Sep 29

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

254 - Early Salvage Stereotactic Radiotherapy (esSBRT) for Biochemical Failure after Radical Prostatectomy: Preliminary Results

01:20pm - 01:30pm ET

Room 210

Presenter(s)

Marta Bottero, MD, PhD - Regina Elena National Cancer Institute, Rome, Rome

M. D. R. I. Bottero¹, A. Magli², L. Tagliaferri³, E. Villa⁴, R. Mazzola⁴, E. Ali'⁵, S. Vagge⁶, F. Trippa⁷, N. Simoni⁸, A. Faiella⁹, A. Farneti⁹, and G. Sanguineti¹; ¹Department of Radiation Oncology, IRCCS Regina Elena National Cancer Institute, Rome, Italy, ²Azienda Sanitaria-Universitaria Giuliano Isontina, Radiation Oncology, Trieste, Italy, ³Fondazione Policlinico Agostino Gemelli IRCCS, UOC Radiation Oncology, Rome, Italy, ⁴Humanitas Gavazzeni, U.O. Radiation Oncology, Bergamo, Italy, ⁵Azienda USL-IRCCS Reggio Emilia, Radiation Oncology Unit, Reggio emilia, Italy, ⁶E.O. Ospedali Galliera, Department of Radiation Oncology, Genoa, Italy, ⁷S. Maria Hospital, Radiotherapy Oncology Centre, terni, Italy, ⁸AOU Parma, Parma, Italy, ⁹IRCCS Regina Elena National Cancer Institute, Radiation Oncology, Rome, Italy

Purpose/Objective(s):

To assess the efficacy of ultra-hypofractionated salvage radiotherapy (RT) in 5 fractions (fxs) for biochemical failure after radical prostatectomy (RP).

Materials/Methods:

This is a multicenter phase II study enrolling patients with biochemical failure after RP defined as 2 consecutive PSA rises above 0.2 ng/ml and no regional/distant metastases at restaging prostate-specific membrane antigen positron emission tomography (PSMA PET). Exclusion criteria included pN+ at RP, previous pelvic radiotherapy/androgen deprivation therapy (ADT) and serum PSA higher than 2 ng/ml at enrollment. Local restaging with multiparametric magnetic resonance imaging (mpMRI) was optional. esSBRT consisted of 30 Gy to the prostatic bed (PB) in 5 fxs delivered every other day or weekly. Macroscopic local disease in the PB at mpMRI, if present, received a simultaneous boost to 40 Gy/5 fxs. Patients with ISUP 4-5 or pT3b at RP or PSA>1 ng/mL at enrollment received elective pelvic nodal treatment (25 Gy/5 fxs) and 6 months of ADT. The primary endpoint was freedom from biochemical failure (FFBF) defined as a PSA increase of at least 0.2 ng/ml over PSA nadir. The target accrual was 103 patients (pts). Patients with biochemical failure were restaged with PSMA PET per protocol. Survival curves were calculated with the Kaplan Meier method.

Results:

Between September 2022 and July 2025, 103 patients were accrued from 6 Institutions. Median follow-up is 16.0 months (IQR: 8.2-26.2 mths). All pts were treated to 30 Gy to the PB; 52/83 (62.5%) received a boost to the presumed local failure at mpMRI; 14/103 (13.6%) were also treated on the pelvic nodes and received short term ADT. The median time from surgery to RT was 38.6 months (IQR: 21.1-67.6 mths) and the median pre-RT PSA was 0.41 ng/mL (IQR: 0.29-0.61 ng/ml). Nineteen pts failed biochemically at a median time of 10.3 months (IQR 6-16.3 mths). The 2-yr FFBF is 73.4% (95%CI: 61.4%-85.4%). At restaging PSMA PET, the pattern of failure was as it follows: biochemical only 4 pts (3.9%); rT1c 1 pt (1.0%); rN1 11 pts (10.7%); rM1a 1 pt (1.0%); rM1b 2 pts (1.9%). Only one patient failed within the treated volume.

Conclusion:

esSBRT in 5 fractions is highly effective within the treated volume, providing acceptable biochemical control rates. However, the number of early clinical relapses within the untreated pelvis, despite baseline PSMA PET and risk-adapted volume selection is a concern and warrants further investigation.