Prostate-specific antigen kinetics following hypofractionated stereotactic body radiotherapy versus conventionally fractionated external beam radiotherapy for low- and intermediate-risk prostate cancer.

Objective: The purpose of this study was to compare the prostate-specific antigen (PSA) kinetics between stereotactic body radiotherapy (SBRT) using Cyberknife and conventionally fractionated external beam radiotherapy (CF-EBRT) in low- and intermediate-risk prostate cancer.

Methods: A total of 69 patients with low- and intermediate-risk prostate cancer were enrolled. Thirty-four patients were treated with SBRT (36.25 Gy in five fractions) using Cyberknife and 35 patients treated with CF-EBRT (70.2-75.6 Gy in 39-42 fractions). PSA nadir, rate of PSA decline and biochemical failure (BCF) free survival were calculated and compared.

Results: With a median follow-up of 53.6 months (range, 14-74), the median slopes for SBRT were -0.430, -0.199, -0.127 and -0.094 ng/mL/month, respectively, for durations of 1, 2, 3 and 4 years following radiotherapy. Similarly, for CF-EBRT, the median slopes were -0.529, -0.138, -0.109 and -0.056 ng/mL/month, respectively. The slope of CF-EBRT was significantly different with a greater median rate of change for 1 year than SBRT (P = 0.018). Conversely, the slopes of SBRT for duration for 2, 3 and 4 year tended to be continuously greater than CF-EBRT (P = 0.028, P = 0.058 and P = 0.128, respectively). The significantly lower PSA nadir was observed in SBRT (nadir 0.23 ng/mL) compared with CF-EBRT (nadir 0.37 ng/mL) (P = 0.011). Five-year BCF free survivals were 100% for SBRT and 80.8% for CF-EBRT (P = 0.031).

Conclusions: Patients treated with SBRT experienced a lower PSA nadir and tended to a continuously greater rate of decline of PSA for duration 2, 3 and 4 years than CF-EBRT. The improved PSA kinetics of SBRT leaded to favorable BCF-free survival.