Table 1: Patient characteristics according to pre-SRT serum calcium level.

VariablePre-SRT serum calcium levelP value
Low: ≤9.0 mg/dL
Moderate: >9.0 and ≤9.35 mg/dL High: >9.35 mg/dL

Pre-RP PSA level (ng/mL)11.0 (3.4, 32.5)11.1 (2.6, 56.7)7.3 (2.0, 44.4)0.29
Pre-SRT PSA level (ng/mL)0.7 (0.2, 15.3)0.6 (0.2, 36.1)0.8 (0.1, 4.9)0.12
SRT dose (Gy)64.8 (60.0, 70.2)64.8 (58.4, 70.2)66.6 (54.0, 72.4)0.16
Age at SRT initiation67 (48, 80)68 (55, 79)68 (44, 85)0.38
Time from RP to SRT initiation (months)22 (<1, 117)20 (2, 126)24 (3, 181)0.50
Time from serum calcium measurement to SRT initiation (days)16 (1, 362)21 (<1, 361)21 (<1, 362)0.73
Pathological tumor stage0.68
 T222 (45%)24 (41%)28 (49%)
 T3a18 (37%)20 (34%)16 (28%)
 T3b9 (18%)15 (25%)13 (23%)
Surgical margin0.66
 Positive27 (57%)34 (58%)37 (65%)
 Negative20 (43%)25 (42%)20 (35%)
Gleason score0.49
 3–617 (38%)18 (31%)22 (39%)
 719 (42%)26 (45%)25 (45%)
 8–109 (20%)14 (24%)9 (16%)
Pre-SRT hormone therapy0.81
 Yes7 (14%)10 (17%)11 (19%)
 No42 (86%)49 (83%)46 (81%)
Year of start of SRT0.29
 1987–199212 (24%)16 (27%)14 (25%)
 1993–199718 (37%)13 (22%)12 (21%)
 1998–200116 (33%)14 (24%)10 (18%)
 2002–20083 (6%)16 (27%)21 (37%)

The sample median (minimum and maximum) is given for continuous variables. P values result from Fisher’s exact test or a Kruskal-Wallis rank sum test. Information was not available for the following variables: preoperative PSA (low: 7, moderate: 2, and high: 6), surgical margin (low: 2), and Gleason score (Low: 4, Moderate: 1, High: 1). RP: radical prostatectomy. PSA: prostate specific antigen. SRT: salvage radiation therapy.