Pilot Study of the Mirabilis System Prototype for Rapid Noninvasive Uterine Myoma Treatment Using an Ultrasound-Guided Volumetric Shell Ablation Technique

Abstract

Study objective: The primary objective of this pilot study was to evaluate the safety and acute tissue ablation efficacy of a transabdominal high-intensity focused ultrasound (HIFU) prototype device that uses ultrasound imaging guidance for rapid noninvasive ablation of uterine myomas. The secondary objective was to assess preliminary myoma-related symptom improvement and myoma volume reduction at 3 to 6 months post-treatment in subsets of patients.

Design: Multicenter prospective single-arm pilot study (Canadian Task Force classification II-2).

Setting: University-affiliated teaching hospital and private community hospital.

Patients: Women with a diagnosis of symptomatic uterine myomas planning to undergo hysterectomy.

Interventions: Seventy-three women underwent transabdominal ultrasound-guided HIFU treatment using a volumetric ablation technique referred to as "shell ablation," in which the HIFU energy is deposited in patterns that partially encapsulate the peripheral region of the targeted myoma(s). Patients were divided into 2 sequential cohorts, the development cohort (the first 37 patients treated) and the validation cohort (the final 36 patients treated). Development cohort treatments were performed for dose-ranging purposes to identify the optimum HIFU treatment parameters, whereas the validation cohort treatments were performed to validate these final settings. Sixty-five patients (89.0%) received only prophylactic oral, sublingual, or intramuscular analgesia before treatment, sometimes with oral anxiolytics. The remaining 8 patients (11.0%) were anesthetized before treatment. Sixty-seven patients (91.8%) then had scheduled hysterectomies between 0 and 179 days after treatment completion. Adverse events were monitored until study exit, which ranged from 10 to 191 days post-treatment.

Measurements and main results: The primary efficacy endpoint measured in all 73 patients was the nonperfused volume (NPV) of tissue produced, which was assessed between 0 and 7 days post-treatment either by tissue sectioning after hysterectomy or by gadolinium-enhanced magnetic resonance imaging. Secondary efficacy endpoints were also measured in subsets of patients who were prospectively scheduled for delayed hysterectomies: Changes in menstrual blood loss (MBL), symptom severity (SS), and quality of life (QOL) scores were assessed using validated techniques at 3 months post-treatment in 10 patients and changes in treated myoma volume were assessed using magnetic resonance imaging at 3 to 6 months post-treatment in 14 patients. In all 73 patients, there were no reports of any serious adverse device effects, including no damage to any extrauterine collateral tissues or the abdominal skin. In the development cohort, a mean NPV of 17.9 ± 24.9 cm³ (range, 0-123.0) was produced in a mean total treatment time of 4.9 ± 2.4 minutes (range, 1.1-11.3). These metrics improved in the validation cohort, where a mean NPV of 44.9 ± 58.5 cm³ (range, 0-284.7) was produced in a mean total treatment time of 3.6 ± 2.1 minutes (range, 1.5-9.5). In the subsets of patients with data available, there was a significant improvement in QOL score (median, 16.5 point increase; p = .011), an improving trend in SS score (median, 13.5 point decrease; p = .254), and a significant improvement in treated myoma volume (mean, 24.0% decrease; p = .013). In 8 patients who had above-average MBL scores at baseline and regular menstrual cycle lengths during follow-up, there was also a significant improvement in MBL score (median, 40.8% decrease; p = .035).

Conclusion: Ultrasound-guided HIFU ablation with the prototype device demonstrated an excellent safety profile and produced clinically relevant NPVs in a mean total treatment time of under 4 minutes using the final validated treatment settings. Short-term clinical efficacy metrics assessed in subsets of patients were encouraging, and larger studies should be conducted to confirm these results (ClinicalTrials.gov, NCT01946178).

Keywords: Ablation; Fibroid; High-intensity focused ultrasound; Leiomyoma; Menorrhagia; Myoma; Noninvasive; Outpatient; Transabdominal; Ultrasound guided; Ultrasound imaging; Uterine sparing.