Prostate-specific antigen kinetics following hypofractionated stereotactic body radiotherapy for low- and intermediate-risk prostate cancer

Background

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 hypofractonated SBRT in low- and intermediate-risk prostate cancer.

Methods

From 2008 to 2014, 36 patients newly diagnosed, low- and intermediate-risk (NCCN definition) prostate cancer were treated with SBRT using Cyberknife. Total dose of 36.25 Gy in 5 fractions of 7.25 Gy were administered. No one received androgen deprivation therapy (ADT). PSA nadir and rate of change in PSA (slope) were calculated and compared.

Results

With a median follow-up of 52 months (range, 13–71), the median rates of decline of PSA were −0.359, −0.199 and −0.127 ng/mL/month, respectively, for durations of 1, 2 and 3 years after radiotherapy, respectively. The decline of PSA was maximal in the first year and continuously decreased for durations of 2 and 3 year. The median PSA nadir was 0.27 ng/mL after a median 33 months. 5-year biochemical failure (BCF)-free survival was 100% for low- and intermediate-risk patients.

Conclusions

In this report of low- and intermediate-risk prostate cancer, continuous decrease of PSA level for duration 1, 2 and 3 year following SBRT using Cyberknife resulted in lower PSA nadir. Also, SBRT leaded to long-term favorable BCF-free survival in low- and intermediate-risk prostate cancer.