Original Article Prostate-specific antigen kinetics following hypofractionated stereotactic body radiotherapy boost as post-external beam radiotherapy versus conventionally fractionated external beam radiotherapy for localized prostate cancer Jeong Hoon Phak, Hun Jung Kim * , Woo Chul Kim Department of Radiation Oncology, Inha University Hospital, Inha University of Medicine, Inchon, South Korea article info Article history: Received 14 September 2015 Received in revised form 12 November 2015 Accepted 30 November 2015 Available online 12 December 2015 Keywords: Cyberknife Prostate cancer PSA kinetics PSA nadir Stereotactic body radiotherapy abstract Background: Stereotactic body radiotherapy (SBRT) has emerged as an effective treatment for localized prostate cancer. The purpose of this study was to compare the prostate-specific antigen (PSA) kinetics between conventionally fractionated external beam radiotherapy (CF-EBRT) and SBRT boost after whole pelvis EBRT (WP-EBRT) in localized prostate cancer. Methods: A total of 77 patients with localized prostate cancer [T-stage, T1eT3; Gleason score (GS) 5 e9; PSA < 20 ng/mL] were enrolled. A total of 35 patients were treated with SBRT boost (21 Gy in 3 fractions) after WP-EBRT and 42 patients were treated with CF-EBRT (45 Gy WP-EBRT and boost of 25.2e30.6 Gy in 1.8-Gy fractions). PSA nadir and rate of change in PSA (slope) were calculated and compared. Results: With a median follow-up of 52.4 months (range, 14e74 months), the median PSA nadir and slope for SBRT boost were 0.29 ng/mL and 0.506, 0.235, 0.129, and 0.092 ng/mL/mo, respectively, for durations of 1 year, 2 years, 3 years, and 4 years postradiotherapy. Similarly, for CF-EBRT, the median PSA nadir and slopes were 0.39 ng/mL and 0.720 ng/mL/mo, 0.204 ng/mL/mo, 0.121 ng/mL/mo, and 0.067 ng/mL/mo, respectively. The slope of CF-EBRT was significantly different with a greater median rate of change for 1 year postradiotherapy than that of SBRT boost (P ¼ 0.018). Contrastively, the slopes of SBRT boost for durations of 2 years, 3 years, and 4 years tended to be continuously greater than that of CF-EBRT. The significantly lower PSA nadir was observed in SBRT boost (median nadir 0.29 ng/mL) compared with CF-EBRT (median nadir 0.35 ng/mL, P ¼ 0.025). Five-year biochemical failure (BCF) free survival was 94.3% for SBRT boost and 78.6% for CF-EBRT (P ¼ 0.012). Conclusion: Patients treated with SBRT boost after WP-EBRT experienced a lower PSA nadir and there tended to be a continuously greater rate of decline of PSA for durations of 2 years, 3 years, and 4 years than with CF-EBRT. The improved PSA kinetics of SBRT boost over CF-EBRT led to favorable BCF free survival. Copyright © 2015 Asian Pacific Prostate Society, Published by Elsevier. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction Prostate cancer is the most common cancer and the second leading cause of death among men in the United States 1 and the incidence rates in Korea are relatively lower than those in western nations. However, they continue to increase annually owing to the aging of society, adoption of westernized lifestyle, and addition of the prostate-specific antigen (PSA) screening test to the National Cancer Screening Program. 2 As the prevalence of prostate cancer increases, various treatment modalities are considered. External beam radiotherapy (EBRT) is a conventional treatment option for localized prostate cancer. 3 Accumulating recent clinical evidence has demonstrated that that the a/b ratio of prostate cancer is around 2 Gy and lower than that of the surrounding normal tissue. 4,5 The hypofractionated radiotherapy schema may improve the biochemical control of prostate cancer without increasing toxicities associated with late- * Corresponding author. Department of Radiation Oncology, Inha University Hospital, 7-206, Shinheung-dong 3 Ga, Jung-ku, Inchon, 400-711, South Korea. E-mail address: cancerovercome@gmail.com (HJ Kim). Contents lists available at ScienceDirect Prostate International journal homepage: http://p-international.com http://dx.doi.org/10.1016/j.prnil.2015.12.001 p2287-8882 e2287-903X/Copyright © 2015 Asian Pacific Prostate Society, Published by Elsevier. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/). Prostate Int 4 (2016) 25e29