Marieke van Son

146 CHAPTER 8 Table 2 – Multivariable Cox proportional hazards regression analysis for biochemical recurrence for model 1 and model 2 Model 1 Model 2 Candidate predictor Corrected* β-coefficient Corrected* HR (95% CI) p-value Corrected # β-coefficient Corrected # HR (95% CI) p-value Age (years) -0.065 0.94 (0.90-0.98) 0.003 -0.087 0.92 (0.87-0.96) 0.0005 Pre-salvage PSADT (months) Pre-salvage PSADT’ (months) $ -0.14 0.16 0.87 (0.83-0.92) 1.18 (1.09-1.27) <0.0001 <0.0001 -0.12 0.15 0.89 (0.83-0.94) 1.16 (1.07-1.26) 0.0001 0.0004 Pre-salvage PSA (ng/ml) (natural logarithm) 0.78 2.19 (1.50-3.18) 0.0001 1.50 4.47 (2.94-6.80) <0.0001 Seminal vesicle involvement X X X 0.40 1.49 (0.87-2.55) 0.14 GTV (cm 3 ) 0.053 1.05 (1.00-1.11) 0.037 X X X D95% CTV (Gy) NA NA NA X X X Time to PSA nadir post-salvage (months) NA NA NA -0.20 0.82 (0.76-0.88) <0.0001 PSA reduction post-salvage (%) NA NA NA -0.021 0.98 (0.97-0.99) 0.0003 Baseline survival model 1: S 0 (12) = exp(-12.82); S 0 (24) = exp(-65.71); S 0 (36)= exp(-159.00). Baseline survival model 2: S 0 (12) = exp(-214.58); S 0 (24) = exp(- 1869.63); S 0 (36)= exp(-5167.25). *Corrected for optimism with shrinkage factor = 0.845. # Corrected for optimism with shrinkage factor = 0.812. $ PSADT is modelled using restricted cubic splines (3 knots at 10 th , 50 th , and 90 th 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 D. NA = not applicable. X = excluded using backward elimination based on AIC. Abbreviations: 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. S 0 (t)=baseline survival at time point t.