Toroidal Transducer for Intraoperative Thermal Ablation of Pancreatic Tumours by High-Intensity Focused Ultrasound. First In Vitro Experiments

High-intensity focused ultrasound (HIFU) is produced by ultrasonic transducers usually hemispherical in shape creating elementary lesions with an elliptical volume. These lesions must be placed side by side precisely in order to treat a tumour with safety margins. Recently it has been demonstrated that HIFU transducers with toroidal geometry provide a significant increase in the ablation rate (10.5 cc min−1 for a toroidal transducer vs 0.34 cc min−1 for spherical transducers). The aim of this study is to use this toroidal geometry with electronic beam steering for a possible application to the treatment of pancreatic tumours. Several treatment sequences were tested numerically with a software developed by the laboratory in order to estimate the lesions that can be created using this transducer. In vitro experiments were then performed in order to validate the treatment sequence that has been identified as the more relevant for treating small (10 mm in diameter) pancreatic tumours. The time of exposure was 160 s. Using an acoustic power of 80 W the dimensions of the lesions were a diameter of 18.3±1.1 mm and a depth of 17.0±1.2 mm. These results show that a lesion with dimensions sufficiently can be created with possible application to the treatment of pancreatic tumours with safety margins.