ESTRO 2022 - Abstract Book

S502

Abstract book

ESTRO 2022

commencement of radiation therapy (RT). BF was defined as a PSA 0.4 ng/mL and rising after RT or clinical relapse (macroscopic disease or commencement of therapy). Results Median follow up was 8.0 years (interquartile range 6.4-9.9 years), androgen deprivation therapy was used in 66 (34%) men, and median pre-SRT PSA was 0.18 ng/mL. Adjuvant RT (ART) (n=57) was delivered for high risk pathological features with a pre-RT PSA ≤ 0.1 ng/mL, early SRT (n=141) was delivered for a rising or persistent PSA with pre-RT PSA ≤ 0.2 ng/mL, and late SRT (n=95) was delivered for a pre-RT PSA >0.2 ng/mL. From date of commencing RT, the 5/10 year rate of FFBF, DM, CSM, and OS for SRT patients were 72%/57%, 95%/91%, 0%/5% and 96%/87% respectively. Corresponding rates according to ART, early SRT and late SRT category are provided in the table. We found that the final nomogram score was a predictor for BF in patients undergoing SRT (HR 1.90 [1.32-2.73]; concordance index, 0.58 [SE, 0.03; log-rank P < .001]). The figure shows a calibration plot of the predicted against observed freedom from biochemical failure 10 years after SRT based on the 25 th , 50 th and 75 th percentiles of the risk scores.

Conclusion PPRT using Australian contouring guidelines provides high levels of long-term tumour control. Early SRT provides improved disease control compared to late SRT, with 62% of patients with pre-SRT PSA of ≤ 0.2 ng/mL free of BF at 10 years, compared to 48% of patients with pre-SRT PSA of >0.2 ng/mL. We validated an updated multivariable nomogram incorporating PSA kinetics, finding it predictive of biochemical failure after SRT.

PD-0573 Protective Effect of Metformin for Biochemical Failure post Radical Prostatectomy or Radiation

L. Huynh 1 , E. Keit 1 , E. Huang 2 , R.C. Carillo 2 , T. Ahlering 2 , S. Boyle 3 , C.A. Enke 4 , M.J. Baine 4

1 University of Nebraska Medical Center, School of Medicine, Omaha, USA; 2 University of California, Irvine Medical Center, Urology, Orange, USA; 3 University of Nebraska Medical Center, Urology, Omaha, USA; 4 University of Nebraska Medical Center, Radiation Oncology, Omaha, USA

Purpose or Objective