Prostate-Specific Antigen Kinetics After Hypofractionated Stereotactic Body Radiation Therapy Boost as Post-External Beam Radiation Therapy (EBRT) Versus Conventionally Fractionated EBRT for Localized Prostate Cancer

Abstract

Stereotactic body radiation therapy (SBRT) has emerged as an effective treatment for localized prostate cancer. The purpose of this study was to compare the PSA kinetics between conventionally fractionated external beam radiation therapy (CF-EBRT) and SBRT boost after whole pelvis (WP) EBRT in localized prostate cancer. A total of 77 patients with localized prostate cancer (T1-T3; GS 5-9; PSA<20 ng/mL) were enrolled. Thirty-five patients were treated with SBRT boost (21 Gy in 3 fractions) after WP-EBRT and 42 patients treated with CF-EBRT (45 Gy WP-EBRT and boost of 25.2-30.6 Gy in 1.8 Gy fractions). PSA nadir and rate of change in PSA (slope) were calculated and compared. With a median follow-up of 52.4 months (range, 14-74), 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/month, respectively, for durations of 1, 2, 3 and 4 years post radiation therapy. Similarly, for CF-EBRT, the median PSA nadir and slopes were 0.39 ng/mL and -0.720, -0.204, -0.121 and -0.067 ng/mL/month, respectively. The slope of CF-EBRT was significantly different with a greater median rate of change for 1 year post radiation therapy than that of SBRT boost (P = 0.018). Contrastively, the slopes of SBRT boost for duration for 2, 3 and 4 year tended to 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 0.35ng/mL) (P = 0.025). 5 year biochemical failure (BCF) free survival was 94.3% for SBRT boost and 78.6% for CF-EBRT (P = 0.012). Patients treated with SBRT boost after WP-EBRT experienced a lower PSA nadir and tended to be continuously greater rate of decline of PSA for duration 2, 3 and 4 years than CF-EBRT. The improved PSA kinetics of SBRT boost over CF-EBRT leaded to favorable BCF-free survival.