Prediction models for biochemical failure after FS-HDR-BT 165 Model 2 p-value 0.0005 0.0001 0.0004 < 0.0001 0.14 X X < 0.0001 0.0003 Corrected* HR (95% CI) 0.92 (0.87-0.96) 0.89 (0.83-0.94) 1.16 (1.07-1.26) 4.47 (2.94-6.80) 1.49 (0.87-2.55) X X 0.82 (0.76-0.88) 0.98 (0.97-0.99) Corrected* coefficient -0.087 -0.12 0.15 1.50 0.40 X X -0.20 -0.021 Model 1 p-value 0.003 < 0.0001 < 0.0001 0.0001 X 0.037 NA NA NA Corrected* HR (95% CI) 0.94 (0.90-0.98) 0.87 (0.83-0.92) 1.18 (1.09-1.27) 2.19 (1.50-3.18) X 1.05 (1.00-1.11) NA NA NA Corrected coefficient -0.065 -0.14 0.16 0.78 X 0.053 NA NA NA Candidate predictor Age (years) Pre-salvage PSADT’ (months) Pre-salvage PSADT” (months)$ Pre-salvage PSA (ng/mL) (natural Seminal vesicle involvement GTV (cm3) D95% CTV (Gy) Time to PSA nadir post-salvage (months) PSA reduction post-salvage (%) Baseline survival model 1: S0(12) = exp(-12.82); S0(24) = exp(-65.71); S0(36)= exp(-159.00). Baseline survival model 2: S0(12) = exp(-214.58); S0(24) = exp(-1869.63); S0(36) = exp(-5167.25). *Corrected for optimism with shrinkage factor = 0.845. #Corrected for optimismwith shrinkage factor = 0.812. $PSADT is modelled using restricted cubic splines (3 knots at 10th, 50th, and 90th percentile), resulting in one extra parameter, PSADT’ , which is dependent on PSADT and can be calculated according to the formula for PSADT’ in Supplementary File E. NA = Not applicable. X = Excluded using backward elimination based on AIC. Legend: HR = Hazard rate. CI = Confidence interval. PSA = Prostate-specific antigen. FS-HDR-BT = Focal salvage high-dose-rate brachytherapy. PSADT = PSA-doubling time. GTV = Gross Tumour Volume. D95% = Dose to 95% of the volume. CTV = Clinical Target Volume. S0(t) = Baseline survival at time point t. Table 2 – Multivariable Cox proportional hazards regression analysis for biochemical recurrence 8
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