The 15-year outcomes of high-dose-rate brachytherapy for radical dose escalation in patients with prostate cancer - a benchmark for high-tech external beam radiotherapy alone?

Abstract

Purpose: Dose escalation using high-dose-rate brachytherapy (HDR-BT) is an established treatment method for prostate cancer. First, long-term results were previously published (specific Kiel method). This study aims to evaluate 10-/15-year outcomes of Kiel Protocol 1 (1986-1992).

Methods and materials: Conformal external beam radiotherapy (EBRT) was delivered to the pelvis (50 Gy per conventional fractionation) along with an HDR boost to the prostate amounting to a combined biologic equivalent dose in 2 Gy per fraction of 117.25 Gy (α/β = 3). The HDR-BT was performed in two fractions of 15 Gy to the peripheral zone of McNeal. The EBRT-clinical target volume covered the full pelvis. The analyzed cohort totaled 122 patients. The reported end points were overall/cancer-specific survival, local recurrence/distant metastasis rates, and biochemical (BC) control rates according to American Society for Therapeutic Radiology and Oncology/Phoenix definitions. All end points were calculated using the Kaplan-Meier method and the log-rank test in univariate analyses.

Results: The mean follow-up time was 116.8 months. The 5-, 10-, and 15-year survival rates were 81%, 62.1%, and 45% for overall survival; 92.1%, 83.1%, and 75.3% for cancer-specific survival; 92.5%, 91.4%, and 83.9% for local recurrence-free survival; and 83.8%, 81.2%, and 69.8% for distant metastasis-free survival, respectively. American Society for Therapeutic Radiology and Oncology-defined BC tumor control rates at 5, 10, and 15 years were 81.1%, 74%, and 67.8%, respectively. According to Phoenix, the BC control rates at 5, 10, and 15 years were 77.8%, 69%, and 63.6%, respectively.

Conclusions: The long-term results for the combination of HDR-BT and EBRT continue to show excellent results, providing high equivalent dose in 2 Gy per fraction and high disease control rates. These outcomes were reproducible for the extended follow-up period ranging up to 21.9 years.

Keywords: Dose escalation; HDR brachytherapy; Long-term results; Prostate cancer.