Does Brachytherapy Boost Improve Biochemical Control in Intermediate and High-Risk Prostate Cancer Patients Compared to External Beam Radiotherapy Alone?

Abstract

<h3>Purpose/Objective(s)</h3> The purpose of this analysis was to investigate whether the combination of external beam radiotherapy (EBRT) and brachytherapy boost (EBRT+BT) is superior to EBRT alone in terms of biochemical control (BC) in the management of intermediate (IR) and high risk (HR) prostate cancer (PC) patients and whether the difference is associated with local biologically effective dose (BED) escalation. <h3>Materials/Methods</h3> We investigated 1123 patients treated for IR (24.8%) or HR PC (75.2%) with EBRT (90.7%) or EBRT+BT (9.3%) at one institution between 2003 and 2012. Kaplan-Meier curves were used to calculate biochemical control. Log-rank testing and Cox regression were used to compare results between groups. BED was calculated using α/β of 3 for PC. The majority of patients treated with EBRT received 76 Gy in 2 Gy fractions (79%, median BED = 126.7 Gy) or equivalent. The majority of patients treated with EBRT+BT received either 54 Gy in 2 Gy fractions followed by 10-11 Gy single fraction BT boost (47.6%, median BED = 133.3 Gy), or 46-50 Gy in 2 Gy fx followed by 20-21 Gy two fraction BT boost (51.4%, median BED = 171.2 Gy). <h3>Results</h3> The median age of the patients was 68-years. The 5-year BC was 79%. There was no statistically significant difference in BC between patients treated with EBRT or BT in IR (<i>P</i> = 0.74) and HR (<i>P</i> = 0.73) PC groups. There was a significant difference between patients receiving lower and higher BED (> 135 Gy) fractionation schemes in favor of higher BED, both for IR (5-y BC of 100% vs 81%, <i>P</i> = 0.02) and HR group (5-y BC of 92% vs 77%, <i>P</i> = 0.02). The BED was inversely associated with risk of BC in univariate analysis (HR = 0.98; CI95% 0.97-0.99; <i>P</i> < 0.01), and remained an independent prognostic factor in the multivariate analysis (HR = 0.97; CI95% 0.96-0.99; <i>P</i> < 0.01) along with Gleason Grade Groups score (HR = 1.18; CI95% 1.05-1.32; <i>P</i> < 0.01). <h3>Conclusion</h3> The combination of EBRT and BT boost has the potential to significantly improve biochemical control in IR and HR prostate cancer patients through local BED escalation. The improvement in BC was observed in patients receiving higher BED, as well as a significant association between BED and risk of biochemical failure.