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

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.

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.

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).

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.

Asia-Pacific journal of clinical oncology. 2016 Jul 27 [Epub ahead of print]

Seok Ho Lee, Hun Jung Kim, Woo Chul Kim

Department of Radiation Oncology, Gachon University Gill Medical Center, Inchon, South Korea., Department of Radiation Oncology, Inha University Hospital, Inha University of Medicine, Inchon, South Korea., Department of Radiation Oncology, Inha University Hospital, Inha University of Medicine, Inchon, South Korea.