Salvage radiotherapy after radical prostatectomy 731 Table 2: Univariate and multivariate analysis for the prediction of salvage radiotherapy outcome Prognostic factors Age Pathologic stage Gleason score Negative surgical margins Seminal vesicle invasion Extracapsular invasion Lymphatic vessel invasion Negative vascular invasion Perineural infiltration PSAa doubling time Preradiotherapy PSA level Time from RPb to RTc Time from biochemical failure to RT Prescribed radiation dose Size of radiation field at gantry 0° aPSA = prostate-specific antigen bRP = radical prostatectomy cRT = radiotherapy dCI = confidence interval. Univariate analysis Multivariate analysis Hazard ratio 1.01 1.59 1.62 1.01 4.25 0.18 4.35 0.59 1.97 0.97 1.28 1.00 1.00 0.98 0.99 95% CId 0.95–1.08 1.06–2.40 1.11–2.36 0.44–2.28 1.65–11.00 0.06–0.56 1.86–10.18 0.26–1.34 0.84–4.63 0.88–1.06 0.88–1.86 1.00–1.01 0.99–1.02 0.93–1.02 0.95–1.03 P value 0.832 0.028 0.013 0.998 0.003 0.004 0.001 0.203 0.120 0.461 0.203 0.962 0.903 0.250 0.522 Hazard ratio 0.90 0.54 1.80 11.16 41.67 0.43 500.00 8.04 0.58 1.31 3.54 1.00 1.01 0.85 1.07 95% CI 0.80–1.02 0.13–2.30 1.06–3.07 1.53–81.36 0.01–0.34 0.30–6.15 24.39–12119.75 1.62–40.03 0.12–2.93 0.92–1.87 1.61–7.76 1.00–1.01 0.98–1.04 0.75–0.96 1.01–1.14 P value 0.083 0.398 0.030 0.018 0.006 0.534 <0.0001 0.011 0.508 0.136 0.017 0.671 0.546 0.010 0.047 Fig. 2. Biochemical disease-free survival after salvage radiotherapy following a radical prostatectomy, stratified according to the Gleason score (GS). DISCUSSION The target of salvage RT following RP is to control local recurrence in the prostate bed leading to biochemical failure. However previous studies have reported that almost Fig. 3. Biochemical disease-free survival after salvage radiotherapy following a radical prostatectomy, stratified according to lymphatic vessel invasion (LI). half of patients experience biochemical failure within 5 years [5–8]. Biochemical failure was found to increase the risks of distance metastasis and death [3, 4]. Biochemical failure after salvage RT suggests the presence of cancer cells beyond the radiation field or the presence of residual cancer cells within the radiation field. Patients with a rapid