SABR in High-Risk Prostate Cancer: Outcomes From 2 Prospective Clinical Trials With and Without Elective Nodal Irradiation

Abstract

There is limited data on stereotactic ablative radiation therapy (SABR) in high-risk prostate cancer (PCa), especially regarding the role of elective nodal irradiation (ENI). This study compares 2 prospective phase 2 trials using SABR in high-risk PCa, with and without ENI. Patients had high-risk PCa. Those in trial 1 received 40Gy in 5 fractions to the prostate and 30Gy in 5 fractions to the seminal vesicles. Patients in trial 2 received 40Gy in 5 fractions to the prostate and 25Gy in 5 fractions to the pelvis and seminal vesicles. National Cancer Institute Common Terminology Criteria for Adverse Events toxicities were collected. Biochemical failure (BF) was defined as nadir+2, and the 4-year prostate-specific antigen (PSA) response rate (4yPSARR) was <0.4ng/mL. Sixty patients were included (trial 1, n=30; trial 2, n=30). Median follow-up was 5.6years and 4.0years. The median nadir PSA was 0.02ng/mL for both trials. Six patients had BF, all from trial 1. The BF rate was 14.6% at 5years in trial 1 and 0% in trial 2. Sixty-three percent of patients in trial 1 and 93% in trial 2 had a 4yPSARR. Two patients died in trial 1, 1 from metastatic disease. One patient in trial 2 died of other causes. No other patients developed metastatic disease, and 1 patient in trial 1 had castrate resistant PCa. Overall survival at 5years was 93.2% and 96.7% (P=.86). There was significantly worse late gastrointestinal and sexual toxicity in trial 1, but there was no difference in late genitourinary toxicity. SABR in high-risk PCa yields biochemical control rates that may be comparable to that of other radiation therapy modalities. ENI using SABR is feasible and may lead to a significant improvement in biochemical control and in 4yPSARR, without an increase in late gastrointestinal or genitourinary toxicity. Longer follow-up would provide a better assessment of biochemical control. Well-conducted phase 3 trials are needed to fully establish the role of SABR and ENI in high-risk PCa.