Ten-year outcomes of post prostatectomy radiotherapy and external validation of an updated nomogram
PD-0572
Abstract
Ten-year outcomes of post prostatectomy radiotherapy and external validation of an updated nomogram
Authors: Stephen Chin1,2,3, Patrick Horsley4, Hitesh Mistry5, Noel Aherne1,4, Thomas Shakespeare1,4
1University of New South Wales, Rural Clinical School, Coffs Harbour, Australia; 2La Trobe University, Olivia Newton John Cancer Research Institute, Heidelberg, Australia; 3University of Melbourne, Surgery at Austin Health, Heidelberg, Australia; 4Mid North Coast Cancer Institute, Radiation Oncology, Coffs Harbour, Australia; 5The University of Manchester, Division of Pharmacy and Cancer Sciences, Manchester, United Kingdom
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Purpose or Objective
Long term tumour control outcomes have not been published for post
prostatectomy radiation therapy (PPRT) to the prostate bed using Australian
contouring guidelines. We report 10 year outcomes after PPRT using Australian
contouring guidelines and externally validated a recently updated nomogram (Campbell
et al. 2021) predicting biochemical failure (BF) after salvage radiation
therapy (SRT) incorporating PSA kinetics.
Material and Methods
A retrospective review was performed for 293 men treated with image
guided intensity modulated radiation therapy to the prostate bed with 64-66Gy
in 32-33 fractions for pT2-4 R0-1 N0/X M0 prostate adenocarcinoma. Freedom from
biochemical failure (FFBF), distant metastasis (DM), cancer-specific mortality
(CSM), and overall survival (OS) were analysed from 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 25th,
50th and 75th 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.