Prostate specific antigen kinetics following robotic stereotactic body radiotherapy for localized prostate cancer

Figures & data

Table I. Patient characteristics (n = 175).

Age
median	69
range	48–85
Initial PSA (ng/ml)
median	5.7
range	2.2–32.5
Clinical stage
T1c	119
T2a	25
T2b	14
T2c	5
Gleason score
≤ 6	83
7	78
≥ 8	2
Prostate volume (cm^3)
median	36
range	11.6–138.7
Initial testosterone (ng/dl)
median	316
range	115–1149

Figure 1. Time dependent cohort-averaged PSA (A) and serum testosterone (B) after ultra hypofractionated prostate SBRT.

Figure 2. Box plot of median PSA nadir for entire cohort and as a function of initial PSA and benign PSA bounce. *indicates p-value < 0.05.

Table II. PSA Kinetics.

Median PSA nadir	0.3 ng/ml (0.02–1.8 ng/ml)
PSA nadir ≤ 0.5 ng/ml	70.6%
Median time to nadir	30 months (3–48 months)
PSA bounce	36.2%
Median time to PSA bounce	15 months (1–42 months)

Table III. Predictors of achieving PSA nadir < 0.5 ng/ml.

Univariate logistic regression
Parameter	OR	95% CI	p-Value
Age (years)	1.04	(0.99–1.09)	0.159
Prostate volume (cm^3)	1.0	(0.98–1.02)	0.757
Gleason score
6	1.0
7–10	1.43	(0.73–2.8)	0.298
T stage
T1c	1.0
T2abc	1.97	(0.86–4.5)	0.108
Time to nadir (mos)	1.0	(0.96–1.1)	0.912
Initial testosterone (per 10 ng/dl)	1.0	(0.99–1.1)	0.914
Initial PSA (ng/ml)	0.88	(0.80–0.97)	0.011
Testosterone at nadir (per 10 ng/dl)	0.97	(0.94–0.99)	0.014
PSA bounce	0.32	(0.16–0.64)	0.001

Multivariate logistic regression
Parameter	OR	95% CI	p-Value
Initial PSA (ng/ml)	0.88	(0.79–0.98)	0.022
Testosterone at nadir (per 10 ng/dl)	0.97	(0.94 –0.99)	0.019
PSA bounce	0.29	(0.14–0.61)	0.001

Figure 3. Cohort-average time dependent PSA data (triangles) fit to functional volume PSA model (solid red line) with 95% confidence interval (dashed red line). Inset: Individual patient time-dependent model predicted PSA plotted against actual PSA.