Prostate-specific antigen kinetics following hypofractionated stereotactic body radiotherapy boost and whole pelvic radiotherapy for intermediate- and high-risk prostate cancer.

Aim: Stereotactic body radiotherapy (SBRT) has emerged as an effective treatment for localized prostate cancer. However, prostate specific antigen (PSA) kinetics after SBRT has not been well characterized. The objective of the current study is to analyze the rate of PSA decline and PSA nadir following SBRT boost after whole pelvis radiotherapy (WPRT) in intermediate- and high-risk prostate cancer.

Methods: From March 2008 to July 2014, 42 patients newly diagnosed, intermediate- and high-risk (NCCN definition) localized prostate cancer were treated with SBRT boost using Cyberknife after WPRT. The whole pelvis dose was 45 Gy (25 fractions of 1.8 Gy) and the SBRT boost dose was 21 Gy (3 fractions of 7 Gy). No one received androgen deprivation therapy (ADT) before biochemical relapse. PSA nadir and rate of change in PSA (slope) were calculated and compared.

Results: With a median follow-up of 53.6 months (range, 14-74), the median rates of decline of PSA were -0.605, -0.229 and -0.166 ng/mL/month, respectively, for durations of 1, 2 and 3 years postradiotherapy, respectively. The median PSA nadir was 0.32 ng/mL after a median 36 months. 4-year biochemical failure (BCF) free survival was 100 percent for intermediate-risk and 71.4 percent for high-risk patients (P = 0.002).

Conclusions: In this report of intermediate- and high-risk prostate cancer, continuously greater rates of decline PSA for duration 1, 2 and 3 year following SBRT boost after WPRT resulted in lower PSA nadir. Also, SBRT boost after WBPT leads to favorable BCF-free survival.