Volumetric MR-guided high-intensity focused ultrasound (HIFU) ablation is a safe and effective treatment for large uterine fibroids, offering a noninvasive alternative to uterine fibroid embolization, according to a study published online March 8 in Radiology.
MR-guided HIFU has seen a rapid increase in clinical use due largely to its noninvasive nature and the fact it does not require exposure to ionizing radiation, according to study authors Young-sun Kim, MD, and colleagues at the Samsung Medical Center in Seoul, South Korea. One drawback working against the procedure is the lengthy procedure time due to a small ablation zone and required cooling intervals.
Enter volumetric ablation, which steers the focus of the HIFU beam in outward-moving concentric circles inducing a larger ablation zone and using energy more efficiently. Because heat deposited during sonication to the inner part of the trajectory preheats the outer parts, procedure times can be reduced, explained the authors. They developed a volumetric MR-guided HIFU ablation technique with a one-layer strategy—meaning all treatment cells were placed in one coronal plane--designed to exploit near-field heat accumulation in the treatment of large uterine fibroids (more than 10 cm).
To study the effectiveness of this technique, the authors investigated the outcomes for 27 women with large uterine fibroids treated with volumetric MR-guided HIFU ablation with a one-layer strategy.
All treatments showed technical success in one session, with a mean treatment time of 166 minutes. Immediate nonperfused volume was 64.2 percent of fibroid volume. Three month follow-up showed the mean symptom severity score had decreased from 37.4 at baseline to 24.0. Effectiveness of the technique showed a significant negative correlation with K trans values at baseline dynamic contrast material-enhanced MR imaging.
“Volumetric MR-guided HIFU ablation therapy with a one-layer strategy may be an effective nonsurgical therapeutic modality for use in patients with uterine fibroids larger than 10 cm in diameter that cannot be effectively treated with uterine fibroid embolization or conventional MR-guided HIFU techniques,” wrote the authors.
The researchers explained there is likely a window of therapy parameters—acoustic power, duration of sonication and cooling intervals—for effective and safe treatment using volumetric MR-guided HIFU ablation with a one-layer strategy. Within this range, heat is lethal to fibroid tissue but not harmful to skin, subcutaneous fat or abdominal wall muscles.
“Fortunately, on the basis of the fact that our one-layer strategy was successful in the majority of cases, it seems likely that this window is not narrow and that the current protocol provided by the manufacturer fits into this window,” wrote Kim et al.