Title: Novel, Noninvasive, Rapid Tumor Ablation Technology using Histotripsy Abstract Our goal is to develop a noninvasive ablation technique that can achieve rapid, homogeneous tumor ablation with the ability to overcome the limitations of current tumor interventions. Many cancer patients are not eligible for surgery. Existing minimally invasive and non-invasive tumor interventions have significant limitations that prevent them from being effective at treating tumors near major vessels, large tumors (>3 cm diameter), or tumors with multiple (>3) nodules. Histotripsy is a non-invasive ultrasound ablation technique that produces cavitation to disrupt the target tissue with millimeter precision. Our previous in vivo studies in normal tissues and tumor models have shown 1) homogenous, complete cellular disruption in targeted areas without damaging the overlying tissue, 2) ability to treat tissue adjacent to large vessels, 3) ability to treat ~5 cm diameter tumors within one hour, 4) real-time treatment monitoring with ultrasound imaging, and 5) potential of complete tumor ablation without residual tumor, recurrence, or new metastasis. Further, our recent results show that histotripsy combined with electrical focal steering completely fractionated ~32 mL (~4cm diameter) ex vivo bovine liver within 10 min, more than twice the rate than any current non-surgical intervention method. These results suggest that histotripsy has the potential to significantly improve upon existing tumor intervention methods. For this proposal, the specific aims focus on technical advancements to allow histotripsy to overcome the limitations of current tumor intervention methods with liver cancer as the first target clinical application. The four aims are: 1) develop an electronic focal steering strategy and parameters to achieve rapid (>5mL/min), homogenous ablation of large (>3cm) and multiple (>3) volumes safely through overlying tissue; 2) develop a motion tracking method to achieve rapid and accurate treatment in the presence of breathing motion; 3) design and construct an integrated ultrasound image-guided histotripsy ablation system for human liver cancer patients; and 4) test the in vivo safety and efficacy of the techniques and device from Aims 1-3 for complete liver tumor ablation in a large animal (porcine) liver model and a woodchuck liver tumor model. The proposed technical improvements and the integrated liver ablation system, all validated in vivo, will be essential to advance histotripsy towards future clinical translation to treat liver tumors and could be extended to many other tumor types, including tumors in the kidney, prostate, pancreas, and uterus.