Supplementary Table 1: Clinical, pathological, and SRT information according to PSA at 3-month follow-up (<0.2 ng/ml or >0.2 ng/ml)

PSA at 3-month follow-up after completion of SRT
Variable / PSA < 0.20 ng/ml
(N=89) / PSA ≥ 0.20 ng/ml
(N=114)
Pre-RP PSA (ng/ml) / 7.9 (1.6, 43.3) / 10.3 (2.5, 219.0)
Pre-SRT PSA (ng/ml) / 0.5 (0.2, 20.0) / 0.9 (0.2, 14.4)
Absolute change in PSA from pre-SRT to 3-month follow-up / 0.3 (0.1, 19.9) / 0.4 (0.0, 33.1)
Percentage change in PSA from pre-SRT to 3-month follow-up / -75 (-100, -33) / -43 (-96, 1286)
Change in PSA from pre-SRT to 3-month follow-up
Increased / 0(0%) / 30(26%)
Decreased / 89(100%) / 77(68%)
Constant / 0(0%) / 7(6%)
SRT dose (Gy) / 66.6 (58.4, 72.4) / 64.8 (54.0, 70.2)
Age at start of SRT (years) / 68 (52, 81) / 68 (44, 85)
Time from RP to initiation of SRT (months) / 22.0 (0.2, 162.8) / 19.1 (1.1, 181.5)
Pathologicaltumor stage
T2 / 43(48%) / 48(42%)
T3a / 32(36%) / 37(33%)
T3b / 14(16%) / 27(24%)
T4 / 0(0%) / 1(1%)
Surgical margin
Positive / 49(56%) / 66(59%)
Negative / 39(44%) / 46(41%)
Gleason score
3-6 / 35(42%) / 37(38%)
7 / 39(47%) / 42(43%)
8-10 / 9(11%) / 19(19%)
BCR Risk Score
0 / 16(19%) / 4(4%)
1 / 32(39%) / 22(23%)
2 / 24(29%) / 34(35%)
3 / 9(11%) / 25(26%)
4 / 2(2%) / 10(10%)
5 / 0(0%) / 2(2%)
The sample median (minimum, maximum) is given for numerical variables. Information was unavailable for the following variables: pre-RP PSA (N=19), pathological tumor stage (N=1), surgical margin (N=3), Gleason score (N=22), and BCR Risk Score (N=23). PSA=prostate-specific antigen. SRT=salvage radiation therapy. RP=radical prostatectomy. BCR=biochemical recurrence. BCR Risk Score ranges from 0 to 5, with higher scores indicating an increased risk of BCR, and was calculated based on pre-SRT PSA, pathological tumor stage, and Gleason Score as previously described by Buskirk et al. [7].

Supplementary Table 2: Cumulative incidence of biochemical recurrence (PSA≥0.2 ng/ml) in patients with a PSA<0.2 mg/ml at 3-month follow-up (N=89) and cumulative incidence of initial biochemical control (PSA<0.2 ng/ml) in patients with a PSA≥0.2 ng/ml at 3-month follow-up (N=114)

Cumulative incidence (%), (95% CI) of biochemical recurrence in patients with a PSA<0.2 ng/ml at 3-month follow-up
Time after 3-month follow-up visit / Overall (N=89) / Pathological tumor stage T2 or T3a (N=75) / Pathological tumor stage T3b (N=14)
3 months / 0 (0-4) / 0 (0-5) / 0 (0-23)
6 months / 3 (0-7) / 4 (0-8) / 0 (0-23)
9 months / 10 (4-17) / 8 (2-14) / 21 (0-40)
1 year / 13 (5-20) / 8 (2-14) / 36 (5-56)
2 years / 23 (13-31) / 16 (7-24) / 57 (21-77)
3 years / 31 (20-40) / 26 (14-36) / 57 (21-77)
4 years / 43 (31-54) / 37 (24-49) / 71 (35-87)
5 years / 51 (37-62) / 47 (31-59) / 71 (35-87)
Cumulative incidence (%), (95% CI) of initial biochemical control in patients with a PSA≥0.2 ng/ml at 3-month follow-up
Time after 3 month follow-up visit / Overall (N=114) / Decreasing PSA at 3-month follow-up (N=77) / Increasing or constant PSA at 3-month follow-up (N=37)
3 months / 6 (1-10) / 8 (2-14) / 0 (0-12)
6 months / 23 (15-31) / 32 (20-42) / 0 (0-14)
9 months / 34 (24-43) / 45 (32-55) / 4 (0-12)
1 year / 42 (31-51) / 52 (39-62) / 14 (0-28)
2 years / 48 (37-58) / 60 (46-70) / 14 (0-28)
Biochemical recurrence was defined as a PSA≥0.2ng/ml after 3-month follow-up. Initial biochemical control was defined as a PSA <0.2ng/ml after 3-month follow-up. PSA=prostate-specific antigen. CI=confidence interval.

Supplementary Table 3: Associations with biochemical recurrence (PSA≥0.2 ng/ml) in patients with PSA<0.2ng/ml at 3-month follow-up (N=89) and associations with initial biochemical control (PSA<0.2 ng/ml) in patients with a PSA≥0.2ng/ml at 3-month follow-up (N=114)

Association with BCR in patients with a PSA<0.2ng/ml at 3-month follow-up (N=89)
Variable / RR (95% CI) / P-value
Pre-RP PSA (doubling) / 0.85 (0.61-1.19) / 0.35
Pre-SRT PSA (doubling) / 1.03 (0.76-1.31) / 0.82
PSA at 3-month follow-up (>0.10 ng/ml) / 1.16 (0.34-2.94) / 0.79
SRT dose (per 5 Gy increase) / 1.06 (0.67-1.70) / 0.80
Age (per 10 year increase) / 0.77 (0.45-1.35) / 0.35
Time from RP to initiation of SRT (doubling) / 1.08 (0.92-1.30) / 0.36
Pathological tumor stage / 0.063
T2 / 1.00 (reference)
T3a / 1.23 (0.62-2.46)
T3b / 2.48 (1.11-5.32)
Surgical margin (positive) / 0.89 (0.49-1.62) / 0.69
Gleason score / 0.048
3-6 / 1.00 (reference)
7 / 0.46 (0.23-0.91)
8-10 / 1.13 (0.41-2.62)
BCR Risk Score (per 1 unit increase) / 1.02 (0.74-1.40) / 0.89
Association with initial biochemical control in patients with a PSA≥0.2 ng/ml at 3-month follow-up (N=114)
Variable / RR (95% CI) / P-value
Pre-RP PSA (doubling) / 0.74 (0.56-0.95) / 0.018
Pre-SRT PSA (doubling) / 0.87 (0.67-1.11) / 0.28
Percentage change in PSA from pre-SRT to 3-month follow-up (50% decrease) / 3.06 (1.95-5.11) / <0.001
Decrease in PSA from pre-SRT to 3-month follow-up / 7.84 (2.88-32.24) / <0.001
PSA at 3-month follow-up (<0.40 ng/ml) / 5.23 (2.93-9.74) / <0.001
SRT dose (per 5 Gy increase) / 1.07 (0.71-1.62) / 0.73
Age (per 10 year increase) / 1.37 (0.90-2.16) / 0.15
Time from RP to initiation of SRT (doubling) / 1.20 (1.01-1.43) / 0.77
Pathological tumor stage / 0.33
T2 / 1.00 (reference)
T3a / 1.07 (0.59-1.93)
T3b/T4 / 0.38 (0.16-0.92)
Surgical margin (positive) / 1.06 (0.61-1.86) / 0.49
Gleason score / 0.37
3-6 / 1.00 (reference)
7 / 0.69 (0.36-1.29)
8-10 / 0.46 (0.15-1.14)
BCR Risk Score (per 1 unit increase) / 0.64 (0.46-0.86) / 0.53
Relative risks and p-values result from single variable Cox proportional hazard models. Relative risks correspond to the change given in parenthesis (continuous variables) or presence of the given characteristic (categorical variables). Biochemical recurrence was defined as a PSA ≥0.2 ng/ml after 3-month follow-up. Initial biochemical control was defined as a PSA<0.2 ng/ml after 3-month follow-up. PSA=prostate-specific antigen. BCR=biochemical recurrence. SRT=salvage radiation therapy. RP=radical prostatectomy. RR=relative risk. CI=confidence interval. BCR Risk Score ranges from 0 to 5, with higher scores indicating an increased risk of BCR, and was calculated based on pre-SRT PSA, pathological tumor stage, and Gleason Score as previously described by Buskirk et al. [7].

Supplementary Figure 1: Cumulative incidence of initial biochemical control (PSA<0.4 ng/ml) after 3-month follow-up in patients with a PSA≥0.4 ng/ml at 3-month follow-up according to PSA at 3-month follow-up (N=69)

Supplementary Figure 2: Cumulative incidence of biochemical recurrence (PSA≥0.2 ng/ml) after 3-month follow-up in patients with a PSA<0.2 ng/ml at 3-month follow-up according to pathological tumor stage (N=89)

Supplementary Figure 3: Cumulative incidence of initial biochemical control (PSA<0.2 ng/ml) in patients with a PSA≥0.2 ng/ml at 3-month follow-up according to presence of a decreasing PSA at 3-month follow-up (N=114)

Supplementary Figure 4: Cumulative incidence of initial biochemical control (PSA<0.2 ng/ml) in patients with a PSA≥0.2 ng/ml at 3-month follow-up according to PSA at 3-month follow-up (N=114)

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