Single-fraction HDR brachytherapy combined with SBRT for intermediate and high-risk prostate cancer: Oncologic and patient-reported outcomes from a prospective phase II study.

Abstract

Brachytherapy boost is an established dose-escalation strategy in intermediate- and high-risk prostate cancer, while stereotactic body radiotherapy (SBRT) offers treatment efficiency with favourable radiobiology. We report mature results of a prospective phase II trial combining single-fraction high-dose-rate (HDR) brachytherapy with prostate-only SBRT. Seventy-six patients with intermediate- or high-risk prostate cancer were enrolled between 2019 and 2021. Treatment consisted of MRI-TRUS fusion HDR brachytherapy (15 Gy, single fraction) followed by SBRT (25 Gy in 5 fractions). Androgen deprivation therapy was prescribed according to risk group. The primary endpoint was patient-reported quality of life (EPIC-26, EORTC QLQ-PR25). Secondary endpoints included acute and late genitourinary (GU) and gastrointestinal (GI) toxicity (CTCAE v5), PSA response, biochemical relapse-free survival (bRFS), metastasis-free survival (MFS), and overall survival (OS). With a median follow-up of 48 months, no acute or late grade 3 GI toxicity was observed. Two patients (2.6 %) developed late grade 3 GU toxicity. Acute and late grade 2 GU toxicity occurred in 11.8 % and 28.9 % of patients, respectively. Urinary and bowel quality of life showed a transient and non-significant decline at one month, returning to baseline by six months. The median PSA nadir was 0.04 ng/mL. The 4-year bRFS and MFS were both 91 % (95 % CI 84-98 %). The median PSA at 4 years was 0.06 ng/mL. Single-fraction HDR brachytherapy combined with SBRT achieved high biochemical control with limited toxicity and preserved quality of life, representing an efficient dose-escalation strategy for intermediate- and high-risk prostate cancer.