Introduction

MRI-guided transurethral ultrasound ablation (TULSA) is a novel minimally-invasive technology for ablation of benign and malignant prostate tissue. The transurethral device emits directional ultrasound producing an ablation volume that is shaped to patient-specific anatomy and pathology using active MRI thermometry feedback control. The aim of this multi-center, prospective Phase I study was to assess the safety and feasibility of MRI-guided TULSA for near whole-gland ablation in patients (pts) with localized prostate cancer (PCa).

Methods

This trial treated 30 pts with biopsy-proven organ confined PCa (T1c-T2a, PSA upto 10 ng/ml, Gleason Score 3+3, and upto 3+4 in Canada only). MRI-guided TULSA was delivered with 3 mm margins at the gland periphery, and expected 10% residual viable prostate tissue around the capsule. Primary endpoints were safety (adverse events), and feasibility (spatial precision of conformal ablation). Exploratory outcomes included PSA, quality of life, MRI and 12-core TRUS-guided biopsy.

Results

Median (IQR) age was 69 (67-71) years, with 24 (80%) low-risk and 6 (20%) intermediate-risk cancers and PSA 5.8 (3.8-8.0) ng/ml. Treatment time and prostate volume, respectively, were 36 (26 - 44) min and 44 (38 - 48) cc. Spatial control of thermal ablation was +/- 1.3 mm. Adverse events (CTCAE v4) included urinary tract infections (10 pts G2), acute retention (3 pts G1; 5 pts G2), and epididymitis (1 pt G3). There were no rectal injuries or fistulae observed. Pre-treatment IPSS of 8 (5-13) and IIEF of 13 (6-28) were recovered to, respectively, 6 (4-10) at 3 mo and 13 (5-25) at 12 mo. Median PSA decreased 87% at 1 month (mo), stable to 0.8 (0.6 - 1.1) ng/ml at 12 mo. Positive biopsies at 12 mo show 61% reduction in total cancer length, clinically significant disease in 9/29 pts (31%), and any disease in 16/29 pts (55%). Following positive biopsy results at 12 mo, 3 pts underwent salvage radical prostactetomy, and 1 pt opted for investigational MRI-guided focal laser ablation.

Conclusions

MRI-guided TULSA is a well-tolerated, safe procedure for pts with localized PCa. TULSA can offer a low morbidity profile while keeping post treatment salvage therapy options open if necessary. The multicentre TULSA-PRO Ablation Clinical Trial (TACT) is currently underway, to evaluate safety and effectiveness of whole-gland ablation with reduced margins in 110 pts.

Funding

This study was sponsored by Profound Medical Inc.