MRI-Guided Transurethral Ultrasound Ablation of Prostate Cancer: A Systematic Review - Beyond the Abstract

Magnetic resonance imaging-guided transurethral ultrasound ablation (TULSA) is a minimally invasive procedure that uses directional ultrasound to ablate targeted prostate tissue from within the gland. The procedure is performed within an MRI scanner and uses the TULSA-PRO system to deliver therapeutic ultrasound heating from multiple independent beams at the same time. The procedure is guided and controlled in real-time with MR imaging and thermometry, allowing precise and efficient ablation of target volumes ranging from focal lesions to the whole gland.

The goal of this systematic review was to identify the prostate cancer indications that have been treated with TULSA and to synthesize efficacy, functional, and safety outcomes. We also aimed to create a model for key outcomes as a function of the proportion of the gland that is targeted for ablation.

Across 10 clinical studies that met our inclusion criteria, there were 224 patients that had been treated with TULSA for a variety of indications that included primary prostate cancer, local recurrence, and locally advanced prostate cancer. Across all indications, the PSA reduction was 54%-97% demonstrating consistently effective ablation of prostate tissue. The presence of intraprostatic calcifications at baseline was associated with residual disease at follow-up and therefore represents a key patient selection criterion for TULSA. Treatment plans ranged from focal lesion-based targets up to whole-gland ablation of prostates as large as 125 mL and included sparing of the neurovascular bundles, ejaculatory ducts, and urethral sphincter. The maximum follow-up was 5 years.

Most patients were treated for primary prostate cancer. By 12-24 months after a single TULSA treatment, 7-17% of patients with primary prostate cancer received salvage treatment. Baseline potency was preserved by 75-98% of patients, and pad-free continence was preserved by 92-100%. We identified a linear relationship between freedom from salvage treatment and the fraction of the prostate targeted for ablation, and a sigmoidal relationship for potency preservation indicating that effects on erectile function become apparent when more than 90% of the gland is ablated.

Smaller cohorts of patients were treated for recurrent prostate cancer or to relieve gross hematuria and continuous catheterization secondary to locally advanced prostate cancer. Among patients treated for primary or recurrent prostate cancer, a subgroup also had lower urinary tract symptoms at baseline. 85% of these patients met criteria for symptom improvement, while men who were asymptomatic at baseline remained so at follow-up. In our opinion patients with concurrent prostate cancer and LUTS is an interesting niche for this technique.

Although results for indications other than primary prostate cancer are promising, small sample sizes limit generalizability. Comparative data is not yet available, but two randomized trials against prostatectomy are underway (NCT03668652, NCT05027477). Another limitation is that most of the included primary prostate cancer patients had only a two-year follow-up. However, this review provides important results to help guide treatment decisions and future studies of this emerging modality.

Written by: Chandler Dora, Gina M. Clarke, Gregory Frey, David Sella

Mayo Clinic Florida, Department of Urology, Jacksonville, Florida, United States; Profound Medical, Mississauga, Ontario, Canada; Mayo Clinic Florida, Jacksonville, Florida, United States

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