Comparison Of Psa Slope And Nadir Between Hypofractionated Sbrt And Conventionally Fractionated Ebrt

112 Background: Patients with early stage prostate cancer have a challenge in selecting from a variety of curative radiotherapy options, including external beam radiotherapy (EBRT) and hypofractionated stereotactic body radiotherapy (SBRT). Rapid post-treatment PSA decline and low PSA nadir have been associated with improved clinical outcomes. The purpose of this study was to compare the PSA measurements over time between conventionally fractionated EBRT and SBRT in newly diagnosed localized prostate cancer.104 patients with low to low-intermediate risk prostate cancer (GS 3+3, PSA < 20 or 3+4, PSA < 15) treated with standard fractionated EBRT (> 70.2 Gy, < 76 Gy) without hormones 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. All included patients had at least 1 year of follow up and 3 serial PSAs. 35 patients that were treated with SBRT to the prostate to 38 Gy in 4 daily fractions also met the same criteria. Of these, 47 and 19 patients treated with EBRT and SBRT, respectively, had a yearly increase in PSA follow-up over 3 years. PSA nadir and rate of change in PSA over time (e.g. slope) were calculated from the completion of RT to 1, 2 and 3 years post RT.The median PSA nadir and slope for patients treated with EBRT was 0.80, 0.50, 0.40 ng and ‑0.07, ‑0.02, ‑0.01 ng/ml/month, respectively, for durations of 1, 2 and 3 years post RT. Similarly, for SBRT, the median PSA nadir and slope were 0.73, 0.50, 0.24 ng and ‑0.09, ‑0.06, ‑0.05 ng/ml/month. The PSA slope for SBRT was greater than EBRT (p = 0.001) at 2 and 3 years following RT, although similar during the first year. These results were consistent when limited to patients with more complete PSA follow-up each year, with PSA nadir significantly lower 3 years after treatment with SBRT compared with EBRT (p = 0.03).Patients treated with SBRT experienced a more rapid decline in PSA 2 and 3 years following completion of RT than with EBRT, and for those with continuous long term followup, a lower PSA nadir, consistent with delivery of a higher bioequivalent dose.