Superiority Of Real-Time Adaptive Interstitial High-Dose-Rate Brachytherapy For Localized Prostate Cancer-Five- And 8-Year Outcomes Of Kiel University Hospital Protocols

A series or randomized trials proved superiority of dose escalation versus conventional doses for localized prostate cancer. High-dose-rate brachytherapy (HDR-BT) has been introduced in 1986 and validated during the next two decades at Kiel University Hospital (KUH) as first institution worldwide for local dose escalation to very high total equivalent dose at 2 Gy (EQD2). This report compares outcomes following radical dose escalation by real-time adaptive interstitial HDR-BT with conventional pre-planning at long-term fallow-up FU. Interdigitated with pelvis external beam radiation therapy interstitial HDR-BT was used to escalate the total EQD2 >100 Gy (α/β = 3) in 459 consecutively treated. Eligible for this analysis were patients with a minimum FU of 24 months. The recorded endpoints were ASTRO biochemical control (BC) rates according to D’Amico risk stratification definition, and local tumor control (LC). BC rates were compared by protocol (KUH protocols 1 and 2 for pre-planning versus KUH protocol 3 for real-time adaptive brachytherapy) and stratified by risk (low, intermediate, and high) using Kaplan-Meier and log-rank test. Figure 1: ASTRO biochemical control according D’Amico classification for high risk cohort (Upper line = 83.4% at 5 years for protocol 3 using adaptive image-guided HDR-BT, lower curves = 65%/64% at 5 years for protocol 1 and 2 using older HDR-BT methods, P = 0.037) Mean follow-up was 77 months. For D’Amico classification and across the protocols the 5 and 8-year ASTRO BC survival rates were not different for low risk (LR) with 89.4% to 100% (P = 0.776), and for intermediate risk (IR) 69.7% to 84.6% (P = 0.349), but inferior for pre-planning brachytherapy (KUH 1 and 2) with 59.9% versus 83.4% following real-time adaptive brachytherapy for high risk (HR) (P = 0.037), respectively. The local relapse free survival (LC) was statistically not different between the brachytherapy methods: pre-planning brachytherapy (KUH 1 and 2) with 91.5 - 95% versus 91.4% following real-time adaptive brachytherapy at 5 years, and 90.1 – 94% versus 91% at 8 years, respectively (P = 0.53). The real-time adaptive method of planning and delivery for interstitial HDR brachytherapy seems to be superior to older pre-planned methods in high risk D’Amico patient cohort. However, there was no statistical significance identified in low or intermediate risk D’Amico strata.