Toroidal intra-operative high intensity focused ultrasound transducer for treating liver metastases under ultrasound imaging guidance: Clinical results of Phase II study

Abstract

The aim of this study was to assess the feasibility, safety, and accuracy of HIFU ablation in patients with liver metastases in a prospective phase II trial. The transducer has a toroidal shape (diameter: 70 mm, radius of curvature: 70 mm) and was divided into 32 ring-shaped emitters operating at 2.5 MHz. Thirty-one patients were included. HIFU ablations were created to ablate metastases (up to 30 mm in diameter) with safety margins in all directions. The use of a toroidal transducer enables an ablation rate (10 cc min-1) significantly higher than spherical transducers. Therefore, using electronic focusing of the beam, it was possible to treat all metastases with safety margin without the need to displace the device between HIFU exposures. The exposure time varied from 40 s to 370 s according to the diameter of the metastases to be treated. The dimensions of these HIFU ablations were a diameter of 48 ± 4.9 mm and a long axis of 45 ± 3.4 mm. No damage occurred to neighboring tissues. This study is the first clinical use of intra-operative HIFU in patients with liver metastases.