Refining the definition of biochemical failure in the era of stereotactic body radiation therapy for prostate cancer: The Phoenix definition and beyond

•The Phoenix definition for biochemical failure has a high false positive rate of 30%.•Lower nadir PSA based thresholds has higher false positivity with minimal lead time.•Patients with BCF had significantly lower rates of early PSA decline (rPSA).•Patients with BCF were significantly more likely to reach nPSA + 2 ≥ 18 months.•Proposed criterion (rPSA ≥ 2.6 or time to nPSA + 2 ≥ 18 months) decreased the false positivity of the Phoenix definition to 6.4%.