title: Prostate-specific antigen kinetics following hypofractionated stereotactic body radiotherapy versus conventionally fractionated external beam radiotherapy for low- and intermediate-risk prostate cancer.
abstract: 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.
authors.affiliation: Department of Radiation Oncology, Gachon University Gill Medical Center, Inchon, South Korea.
authors.forename: Seok Ho
authors.initials: SH
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology, Inha University Hospital, Inha University of Medicine, Inchon, South Korea.
authors.forename: Hun Jung
authors.initials: HJ
authors.lastname: Kim
authors.affiliation: Department of Radiation Oncology, Inha University Hospital, Inha University of Medicine, Inchon, South Korea.
authors.forename: Woo Chul
authors.initials: WC
authors.lastname: Kim
mesh_terms: D000368:Aged; D006801:Humans; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D020360:Neoadjuvant Therapy / Q000379:methods*; D010190:Pancreatic Neoplasms / Q000532:radiotherapy*; D017430:Prostate-Specific Antigen / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000601:surgery; D016634:Radiosurgery / Q000009:adverse effects*
chemical_list: D017430:Prostate-Specific Antigen
keywords: Cyberknife; PSA kinetics; PSA nadir; prostate cancer; stereotactic body radiotherapy