Focused ultrasound ablation of solid tumors: Feasibility of planning tissue-selective treatments.

Abstract

e15600 Background: Focused ultrasound (FUS) is a noninvasive, nonionizing, repeatable local ablative therapy that induces mechanical fractionation or thermal necrosis of a variety of solid tumors including hepatocellular carcinoma, prostate cancer, and desmoid fibromatosis. Recent feasibility studies in animal models have demonstrated the possibility of designing focused ultrasound treatments that are selective (e.g. spare healthy tissue, nerves, and blood vessels) due to differences in tissue and tumor mechanical properties. Given wide variation in individual tumor and patient characteristics, mechanics-based predictions of ablation zone features in different tissues under a range of FUS device settings are needed to permit personalized treatment planning. Methods: A finite difference computational method is used to simulate FUS ablation of tissues with variable mechanical properties (shear moduli of 0.6 – 200 kPa) under different FUS sonication parameters (frequency and peak pressure). The model calculates strain fields contributing to tissue ablation in FUS treatments which are used to predict ablation zone radii and boundary characteristics. Simulation predictions in model tissues are then compared to histology obtained from FUS-treated porcine tissue samples with similar mechanical properties. Results: The mechanical properties of model tissues and FUS treatment parameters have distinct effects on predicted minimum ablation zone radii. For example, smaller ablation zone radii are achieved in stiffer vessel wall than liver under given FUS sonication parameters. In each tissue, lower frequency and higher peak pressure FUS sonication predict a larger ablation zone. Combined variation of sonication frequency and peak pressure are found to achieve wider variation in ablation zone radius than previously achieved with frequency variation alone. Predicted ablation zone radii and boundary characteristics are consistent with the observed histology of FUS-treated tissues. Conclusions: Results show that simulations accounting for tissue mechanical properties and device settings can predict tissue selectivity and ablation zone characteristics observed in FUS procedures. This study demonstrates the potential of using noninvasive measurements of tissue and tumor properties obtained, for example, via shear wave elastography, in combination with micromechanical tissue ablation simulations to develop personalized, selective focused ultrasound treatments for solid tumors.