Dose-response with stereotactic body radiotherapy for prostate cancer: A multi-institutional analysis of prostate-specific antigen kinetics and biochemical control.

BACKGROUND AND PURPOSE: The optimal dose for prostate stereotactic body radiotherapy (SBRT) is still unknown. This study evaluated the dose-response relationships for prostate-specific antigen (PSA) decay and biochemical recurrence (BCR) among 4 SBRT dose regimens. MATERIALS AND METHODS: In 1908 men with low-risk (50.0%), favorable intermediate-risk (30.9%), and unfavorable intermediate-risk (19.1%) prostate cancer treated with prostate SBRT across 8 institutions from 2003 to 2018, we examined 4 regimens (35 Gy/5 fractions [35/5, n = 265, 13.4%], 36.25 Gy/5 fractions [36.25/5, n = 711, 37.3%], 40 Gy/5 fractions [40/5, n = 684, 35.8%], and 38 Gy/4 fractions [38/4, n = 257, 13.5%]). Between dose groups, we compared PSA decay slope, nadir PSA (nPSA), achievement of nPSA ≤0.2 and ≤0.5 ng/mL, and BCR-free survival (BCRFS). RESULTS: Median follow-up was 72.3 months. Median nPSA was 0.01 ng/mL for 38/4, and 0.17-0.20 ng/mL for 5-fraction regimens (p < 0.0001). The 38/4 cohort demonstrated the steepest PSA decay slope and greater odds of nPSA ≤0.2 ng/mL (both p < 0.0001 vs. all other regimens). BCR occurred in 6.25%, 6.75%, 3.95%, and 8.95% of men treated with 35/5, 36.25/5, 40/5, and 38/4, respectively (p = 0.12), with the highest BCRFS after 40/5 (vs. 35/5 hazard ratio [HR] 0.49, p = 0.026; vs. 36.25/5 HR 0.42, p = 0.0005; vs. 38/4 HR 0.55, p = 0.037) including the entirety of follow-up, but not for 5-year BCRFS (≥93% for all regimens, p ≥ 0.21). CONCLUSION: Dose-escalation was associated with greater prostate ablation and PSA decay. Dose-escalation to 40/5, but not beyond, was associated with improved BCRFS. Biochemical control remains excellent, and prospective studies will provide clarity on the benefit of dose-escalation.

Discord Among Radiation Oncologists and Urologists in the Postoperative Management of High-Risk Prostate Cancer.

OBJECTIVE: To query specialty-specific differences regarding postoperative radiotherapy (RT) for high-risk prostate cancer. MATERIALS AND METHODS: Electronic mail survey of radiation oncologists (ROs) and urologists. We sought to maximize absolute response number to capture contemporary practice ethos. The outcome of interest was association between response and specialty. Training level/expertise, practice setting, percentage of consultation caseload consisting of high-risk prostate cancer, and nationality were set as effect modifiers for multivariate logistic regression. RESULTS: In total, 846 ROs and 407 urologists responded. ROs were more likely to prefer adjuvant radiotherapy (ART). ART or early salvage radiotherapy (SRT, with early SRT defined as that delivered at prostate-specific antigen<0.2), whereas urologists were more likely to prefer early or delayed SRT (P<0.0001). ROs were more likely to prefer lower PSA thresholds for initiating SRT (P<0.0001), and more likely to recommend ART in the setting of adverse pathologic features or node-positive disease (P<0.0001). Significantly more ROs would recommend concurrent androgen deprivation therapy or pelvic nodal RT in the setting of node-positive or Gleason score 8 to 10 disease (P<0.0001). CONCLUSIONS: Specialty-specific differences were readily elucidated with respect to timing and indications for ART and SRT, as well as for indications for androgen deprivation therapy and nodal RT. These differences are likely to create a sense of dissonance for patients, which may in turn explain the underutilization of postoperative RT in general practice.