Prostate-only Versus Whole-pelvis Radiation with or Without a Brachytherapy Boost for Gleason Grade Group 5 Prostate Cancer: A Retrospective Analysis

Abstract

The role of elective whole-pelvis radiotherapy (WPRT) remains controversial. Few studies have investigated it in Gleason grade group (GG) 5 prostate cancer (PCa), known to have a high risk of nodal metastases. To assess the impact of WPRT on patients with GG 5 PCa treated with external-beam radiotherapy (EBRT) or EBRT with a brachytherapy boost (EBRT + BT). We identified 1170 patients with biopsy-proven GG 5 PCa from 11 centers in the United States and one in Norway treated between 2000 and 2013 (734 with EBRT and 436 with EBRT + BT). Biochemical recurrence-free survival (bRFS), distant metastasis-free survival (DMFS), and prostate cancer-specific survival (PCSS) were compared using Cox proportional hazards models with propensity score adjustment. A total of 299 EBRT patients (41%) and 320 EBRT + BT patients (73%) received WPRT. The adjusted 5-yr bRFS rates with WPRT in the EBRT and EBRT + BT groups were 66% and 88%, respectively. Without WPRT, these rates for the EBRT and EBRT + BT groups were 58% and 78%, respectively. The median follow-up was 5.6 yr. WPRT was associated with improved bRFS among patients treated with EBRT + BT (hazard ratio [HR] 0.5, 95% confidence interval [CI] 0.2–0.9, p = 0.02), but no evidence for improvement was found in those treated with EBRT (HR 0.8, 95% CI 0.6–1.2, p = 0.4). WPRT was not significantly associated with improved DMFS or PCSS in the EBRT group (HR 1.1, 95% CI 0.7–1.7, p = 0.8 for DMFS and HR 0.7, 95% CI 0.4–1.1, p = 0.1 for PCSS), or in the EBRT + BT group (HR 0.6, 95% CI 0.3–1.4, p = 0.2 for DMFS and HR 0.5 95% CI 0.2–1.2, p = 0.1 for PCSS). WPRT was not associated with improved PCSS or DMFS in patients with GG 5 PCa who received either EBRT or EBRT + BT. However, WPRT was associated with a significant improvement in bRFS among patients receiving EBRT + BT. Strategies to optimize WPRT, potentially with the use of advanced imaging techniques to identify occult nodal disease, are warranted. When men with a high Gleason grade prostate cancer receive radiation with external radiation and brachytherapy, the addition of radiation to the pelvis results in a longer duration of prostate-specific antigen control. However, we did not find a difference in their survival from prostate cancer or in their survival without metastatic disease. We also did not find a benefit for radiation to the pelvis in men who received radiation without brachytherapy.