Comparative study of the effects of respiratory motion on in-vivo HIFU treatments in the liver

Current development of HIFU strategies for the treatment of localized abdominal tumors are limited by organ motion during respiration. In preliminary studies, a numerical model simulated the effects of in-vivo movements on HIFU treatments in the liver. It was shown that a HIFU treatment performed during respiration with juxtaposition of millimetrics lesions is modified in shape and homogeneity. Here, we report recent results from a comparative study which evaluated in simulation and in in-vivo experiments, the interest of using, during respiratory, a toroidal-shaped HIFU device developed for the treatment of liver metastases from colorectal cancer. These experiments were performed during an open procedure, on 9 pigs divided into 3 groups. On the first group, a spherical HIFU transducer was used to juxtapose 49 millimetrics lesions in the liver during respiration. The second group was treated during respiration with a 3 MHz toroi?dal-shaped HIFU transducer. The last group (control) was treated during apnea. For each animal, sequences of ultrasound images were acquired in the liver. Then, a combined method of modeling based on ultrasound speckle tracking and BHTE equation resolution, was used to quantify liver motion and to simulate HIFU treatments during breathing. Liver motions were mainly encountered in the cranial-caudal direction with a frequency comparable to the respiratory frequency (f = 0.2 Hz). Magnitude of the motion was 8.2-10.0 mm. Results of the modeling were well fitted to the observations made on in-vivo gross samples. In vivo lesions created with the spherical device were stretched by 64% and then were split in the tissues. The toroidal-shaped HIFU strategy allowed the generation of homogeneous lesions (12% stretching). These results provide a preliminary validation of the method for modeling liver motion effects. This method was used to demonstrate the effectiveness of a new HIFU device which shows promise for HIFU therapy during respiration.