ИСТИНА

Background: Boiling histotripsy (BH) is a HIFU method that uses milliseconds-long (<20 ms) pulses applied at low duty cycle to mechanically ablate targeted tissue. Compared to thermal ablation, BH has potential clinical advantages as it minimizes heat-sink effects and thermal spread, allows for real-time ultrasound feedback via the appearance of echogenic bubbles at the focus, and monitoring treatment outcome through production of a hypoechoic lesion. The method has been successfully used in pre-clinical studies to fractionate kidney and liver tissue ex vivo and in vivo. The goal of this study was to test the feasibility of BH ablation of fresh ex vivo human prostate tissue as a proof of principal for treating benign prostatic hyperplasia and prostate cancer. Material and Methods: Fresh human prostate tissue samples were obtained via rapid autopsy (<24 hours after death, n=4) using an IRB approved procurement program. Tissue was degassed in a polyacrylamide solution for 2 hours, then the final component was added to catalyze the polymerization of the gel containing the tissue (Figure 1A). Embedded tissue was placed in a custom holder submerged in degassed water (Figure 1B). BH pulses (10 ms duration, 1% duty cycle, peak focal pressures of p+=88 MPa, p-=17 MPa, 100 pulses/focus) were delivered to a rectangular grid with 2 mm spacing within the tissue using a 1.5-MHz custom-made transducer (80 mm diameter and 60 mm focal length). Real time-imaging of the sonications and evaluation of the BH treatment outcomes were performed using Verasonics Ultrasound Engines. A L7-4 probe operating in B-mode was oriented perpendicular to the HIFU beam axis and a P7-4 probe operating in B-mode/color Doppler was placed within the central opening of the BH transducer (Figure 1B). Doppler sequences were triggered by the BH driving electronics to generate images right after the end of each BH pulse. Following treatment, tissue was evaluated grossly or formalin-fixed for histologic assessment with H&E staining. Results: During BH sonications, hyperechoic regions were visualized at the focus on B-mode and BH-induced bubbles were also detected using Color Doppler mode (Figure 2). As treatment progressed, hypoechoic regions of tissue appeared suggesting successful tissue fractionation. On gross assessment following treatment, fluid filled volumetric lesions were observed consistent with mechanical ablation without thermal denaturation (Figure 3). On histological analysis, lesions containing completely homogenized cell debris were observed consistent with histotripsy induced mechanical ablation of glandular elements. Close to the edge of the lesion, the regions of completely homogenized tissue were intermixed with regions of intact smooth muscle and collagen fibrils consistent with sparing of fibromuscular elements (Figure 4). Conclusions: These data represent the first successful application of the BH method in ex vivo human prostate tissue and suggest that BH mechanical prostate ablation is feasible. Further work is ongoing to evaluate a prototype preclinical transrectal device while optimizing parameters of the BH pulsing scheme. Acknowledgements/Funding Sources: This study was funded by RFBR 17-54-33034, NIH R21CA219793, and R01EB007643 grants.