MRI-Guided Micro-US Transperineal Focal Laser Ablation for Localized Prostate Cancer: A 1-Year Follow-Up Study

Academic Background

Prostate cancer (PCA) is one of the most common malignancies among men worldwide. With the widespread adoption of prostate-specific antigen (PSA) screening, the diagnosis of low-risk prostate cancer has significantly increased. Although radical treatments (such as prostatectomy or radiotherapy) offer excellent long-term oncologic control, these treatments are often associated with severe side effects, such as urinary incontinence and erectile dysfunction, which significantly impact patients’ quality of life. Therefore, active surveillance has been proposed as an alternative management strategy for indolent prostate cancer. However, even minor disease progression can cause anxiety in patients, leading some to opt for radical treatment during follow-up.

Focal therapy has emerged as a middle ground, aiming to selectively ablate tumor foci while avoiding the side effects of radical treatment. In recent years, MRI-guided focal laser ablation (FLA) has become a focus of research. Although various focal therapy modalities have been shown to be safe and feasible, their efficacy and long-term functional and oncologic outcomes remain variable. Additionally, establishing effective imaging follow-up protocols remains a challenge.

Study Source

This study was conducted by François Cornud, Katelijne De Bie, Luigi Van Riel, Arnaud Lefèvre, Philippe Camparo, and Marc Galiano, affiliated with Clinique de l’Alma in Paris, France, Amsterdam UMC in the Netherlands, and I-Path Institut de Pathologie des Hauts-de-France in Amiens, France. The study was published in Radiology in December 2024.

Study Objective

This study aimed to evaluate the safety, feasibility, and 12-month functional and oncologic outcomes of MRI-guided micro-US transperineal focal laser ablation (FLA) in localized prostate cancer, as well as to assess the accuracy of micro-US in visualizing MRI-detected lesions with a PI-RADS score of 3 or higher.

Study Methods

Study Participants

This prospective, single-center observational study included patients with low- or intermediate-risk localized prostate cancer and lesions with a PI-RADS score of 3 or higher and a maximum tumor length of ≤20 mm, enrolled between July 2020 and June 2023. All participants provided written informed consent.

MRI Protocol and Evaluation

Participants underwent MRI before study inclusion and during follow-up to evaluate prostate lesions. MRI scans were performed using a 1.5T MRI scanner, including standard sequences, diffusion-weighted imaging (DWI), and dynamic contrast enhancement (DCE) sequences. Lesions were scored according to PI-RADS version 2.1, with PI-RADS ≥3 lesions considered clinically significant.

Micro-US Imaging and Biopsies

MRI-detected lesions were localized using a 29 MHz micro-US system (ExactVu), and biopsies were performed under US guidance. Six to nine targeted biopsies were obtained from each lesion, and three to nine systematic biopsies were taken from areas more than 10 mm away from the lesion. Biopsy results were evaluated by an experienced pathologist.

Focal Laser Ablation (FLA) Protocol

FLA was performed using the EchoLaser system, operating at 1064 nm, delivering 5 W of energy with a total dose of 1600–1800 J per fiber per cycle. The procedure was performed by an experienced urologist and radiologist. Initially, a single-fiber mode was used, but the protocol was later changed to a multifiber mode, with fibers spaced 7–8 mm apart and activated simultaneously to expand the ablation zone. For tumors close to the rectal wall, rectoprostatic hydrodissection was performed to ensure a 5–10 mm distance between the rectum and the prostate.

Follow-Up

Follow-up included multiparametric MRI at 4 days, 6 months, and 12 months post-ablation, as well as PSA tests at 6 and 12 months. Biopsies were performed at 12 months to confirm recurrence.

Study Results

Participant Characteristics

The study included 55 male participants with a median age of 70 years and a median PSA level of 7.0 ng/ml. A total of 58 lesions were treated, with 74% having a Gleason score (GS) of 3 + 4 and 17% having a GS of 3 + 3.

Micro-US Imaging and Biopsies

Micro-US successfully visualized 53 (91%) of the MRI-detected lesions. Single-fiber and multifiber FLA were used to treat 21 (36%) and 37 (64%) tumors, respectively. Multifiber FLA produced significantly larger ablation volumes than single-fiber FLA (median volumes of 15 ml and 4.5 ml, respectively).

12-Month Follow-Up Results

At the 12-month follow-up, 17 (49%) of the 35 treated tumors showed recurrence, including 13 in-field and four out-of-field recurrences. The in-field recurrence rate was 56% for single-fiber FLA and 18% for multifiber FLA. Erectile function scores decreased compared to baseline, while urinary function remained stable.

Complications

One severe complication, a rectoprostatic fistula requiring surgical intervention, occurred. Additionally, 10 participants experienced minor complications, such as urinary retention and infection, which were resolved with medical treatment.

Conclusion

Multifiber micro-US-guided FLA is safe and feasible for the treatment of localized prostate cancer, with an 18% recurrence rate at the 12-month follow-up. Although erectile function slightly decreased, urinary function remained stable. The study results indicate that micro-US has high accuracy in localizing and guiding prostate interventions, and the multifiber mode effectively reduces recurrence rates.

Study Highlights

1. High Resolution of Micro-US: The 29 MHz micro-US system significantly improved lesion visibility, reducing the need for MRI and US image fusion.
2. Advantages of Multifiber Mode: Multifiber FLA produced larger ablation volumes, significantly reducing in-field recurrence rates.
3. Safety: Although one severe complication occurred, FLA was generally safe, with most minor complications resolved through medical treatment.

Study Significance

This study provides preliminary evidence for the application of MRI-guided micro-US FLA in the treatment of localized prostate cancer, demonstrating its safety and feasibility. Future studies with larger sample sizes and longer-term oncologic outcomes are needed to determine its broader clinical applicability.