Hypofractionated SBRT versus conventionally fractionated EBRT for prostate cancer: comparison of PSA slope and nadir

Abstract

BackgroundPatients with early stage prostate cancer have a variety of curative radiotherapy options, including conventionally-fractionated external beam radiotherapy (CF-EBRT) and hypofractionated stereotactic body radiotherapy (SBRT). Although results of CF-EBRT are well known, the use of SBRT for prostate cancer is a more recent development, and long-term follow-up is not yet available. However, rapid post-treatment PSA decline and low PSA nadir have been linked to improved clinical outcomes. The purpose of this study was to compare the PSA kinetics between CF-EBRT and SBRT in newly diagnosed localized prostate cancer.Materials/methods75 patients with low to low-intermediate risk prostate cancer (T1-T2; GS 3 + 3, PSA < 20 or 3 + 4, PSA < 15) treated without hormones with CF-EBRT (>70.2 Gy, <76 Gy) to the prostate only, were identified from a prospectively collected cohort of patients treated at the University of California, San Francisco (1997–2012). Patients were excluded if they failed therapy by the Phoenix definition or had less than 1 year of follow-up or <3 PSAs. 43 patients who were treated with SBRT to the prostate to 38 Gy in 4 daily fractions also met the same criteria. PSA nadir and rate of change in PSA over time (slope) were calculated from the completion of RT to 1, 2 and 3 years post-RT.ResultsThe median PSA nadir and slope for CF-EBRT was 1.00, 0.72 and 0.60 ng/ml and -0.09, -0.04, -0.02 ng/ml/month, respectively, for durations of 1, 2 and 3 years post RT. Similarly, for SBRT, the median PSA nadirs and slopes were 0.70, 0.40, 0.24 ng and -0.09, -0.06, -0.05 ng/ml/month, respectively. The PSA slope for SBRT was greater than CF-EBRT (p < 0.05) at 2 and 3 years following RT, although similar during the first year. Similarly, PSA nadir was significantly lower for SBRT when compared to EBRT for years 2 and 3 (p < 0.005).ConclusionPatients treated with SBRT experienced a lower PSA nadir and greater rate of decline in PSA 2 and 3 years following completion of RT than with CF-EBRT, consistent with delivery of a higher bioequivalent dose. Although follow-up for SBRT is limited, the improved PSA kinetics over CF-EBRT are promising for improved biochemical control.

Prostate-specific antigen kinetics after hypofractionated stereotactic body radiotherapy for localized prostate cancer

“…In our study, the rate of PSA decline after SBRT was -0.372, -0.211 and -0.128 ng/mL/month for durations of 1, 2 and 3 years, respectively. Although the direct comparison of rate of PSA decline with other study is not proper, the rate of PSA decline in our study tends to be more rapid than that of Anward et al (28) . Shi et al described that a lower PSA at diagnosis had a lower PSA velocity following radiotherapy (21) .…”

“…Consistently, in our study, the majority of the PSA decline occurred in the !irst year. Anward et al compared the PSA kinetics between hypofractionated SBRT and conventionally fractionated EBRT for localized prostate cancer and reported that the median slopes for SBRT were -0.09, -0.06 and -0.05 ng/ mL/month, respectively, for durations of 1, 2 and 3 years after radiotherapy (28) . In our study, the rate of PSA decline after SBRT was -0.372, -0.211 and -0.128 ng/mL/month for durations of 1, 2 and 3 years, respectively.…”

Hypofractionated stereotactic body radiotherapy in low- and intermediate-risk prostate carcinoma

“…Anwar et al [18] compared the PSA slope between the hypofractionated SBRT and conventionally fractionated external beam radiation therapy (EBRT) for localized prostate cancer and reported that the PSA slope for SBRT was greater than conventionally fractionated EBRT at 2 and 3 years and PSA nadir was significantly lower for SBRT. Katz et al [2] demonstrated that PSA decline steadily after treatment and achieve very low mean levels of 0.25 ng/mL within 4–5 years.…”

A Phase 1/2 Trial of Brief Androgen Suppression and Stereotactic Radiation Therapy (FASTR) for High-Risk Prostate Cancer

“…The availability of daily in-room image guidance with techniques such as fiducial markers or in-room CT (cone beam or helical) combined with intensity modulated delivery has facilitated the safe delivery of high dose per fraction using stereotactic body radiotherapy (SABR) techniques. The use of SABR has been described in prostate cancer (42)(43)(44)(45)(46) and has been demonstrated to be safe for treatment of the prostate in phase 1/2 studies. To date, this SABR approach has not been extended to high-risk patients requiring prophylactic treatment of regional nodes, although hypofractionated regional pelvic radiation in other disease sites (ie neoadjuvant rectal cancer) has been shown to be safe and well tolerated (47)(48)(49)(50)(51).…”