PROJECT SUMMARY First line radical treatments for localized prostate cancer are associated with significant morbidity and side effects impacting urinary, bowel, and sexual quality of life. As a result, there is strong interest in focal therapy in which the cancer tissue is eradicated while sparing normal healthy prostate and adjacent structures (such as urinary sphincter, rectum, and neurovascular bundles) in order to maintain oncologic outcomes while reducing side effects. To date, clinically available focal therapies rely on thermal ablation (heating or freezing) to induce coagulative necrosis and cell death. Presently, the most widely used thermal technique for focal therapy of prostate cancer is transrectal high intensity focused ultrasound (HIFU). While existing data suggest that thermal HIFU has less morbidity than radical treatments, its ability to effectively control cancer is still uncertain with series reporting positive biopsies in up to 30-40% of patients within one year of treatment. Limitations of thermal HIFU systems, including heat diffusion/sinking and minimal real-time treatment feedback, may explain efficacy concerns. Our team has developed a HIFU-based method termed boiling histotripsy (BH) that uses sequences of milliseconds long HIFU pulses with shock fronts to mechanically ablate targeted tissue to subcellular debris without thermal effects and with real-time ultrasound imaging feedback. We have developed the first prototype of a pre-clinical system and have demonstrated the feasibility of transrectal BH for non-thermal ablation of prostate tissue in a canine model. The specific aims of this proposal are built upon the previous work to refine BH technology into a clinically viable format for focal therapy of PCa. In Aim 1, a novel transrectal multi-element array transducer will be developed and built facilitating efficient volumetric BH prostate ablation using electronic steering and mechanical translation of the focus. The BH transducer will be combined with an imaging probe and both will be controlled by a Verasonics Flexible Ultrasound platform. Comprehensive acoustic characterization of the BH system will be performed, and BH treatment protocols will be designed accordingly and evaluated in tissue phantoms and ex vivo prostate tissue. In Aim 2, improved ultrasound-based imaging algorithms will be developed to enable pre-treatment tumor localization using shear wave elastography and quantitative tissue liquefaction feedback using plane wave Doppler imaging. In Aim 3, the resulting BH array system, exposure protocols, and imaging algorithms will be evaluated in a series of acute and chronic in vivo studies in a canine model to demonstrate the safety and efficacy of the device. At the conclusion of the project period, transrectal BH technology will be ready for submission to FDA for an Investigational Device Exemption in preparation for future clinical trials.