Abstract No. 334 Safety of Histotripsy Treatments of Gas-Filled Colon and Small Bowel in an Ex Vivo Swine Model

Histotripsy is an emerging focused ultrasound therapy which mechanically destroys target tissue. Prior preclinical work suggests that treatment of bowel can be safe in the absence of gas, but the effects of treating near gas-filled bowel are unknown. The purpose of this study was to evaluate the effects of histotripsy on gas-filled colon and small bowel (SB) in an ex vivo swine model using a clinical grade therapy system. Histotripsy (Cloudbreak, HistoSonics Inc.) was performed on colon and SB harvested from healthy swine. The tissue was inflated with room air (4 cm diameter colon, 2 cm SB) and positioned in a degassed water bath lateral to a 1.5% agar phantom. A 2.5 cm diameter sphere was planned in each phantom, with 0.5 cm of the volume extending beyond the edge of the phantom and into the ex vivo tissue, mimicking a clinically relevant margin (n=6 treatments for colon and SB each). Successful targeting of the ex vivo tissue was confirmed by measuring the resulting treatment zone within the phantom and observing that the mediolateral treatment diameter extended beyond the edge of the phantom. Following treatment, tissue was visually inspected, and treated and untreated control samples were submitted for histology. Tissue was successfully targeted in 5/6 colon samples and 6/6 SB samples. No visible signs of damage or air leaks were observed in any treated tissues (0/6 colon; 0/6 SB). Histologic findings are summarized in Table 334.1. In the colon samples, one instance of focal submucosal damage without involvement of lamina propria or mucosa was observed. In SB, small foci showing loss of cytoplasmic detail (< 3 mm) of the muscularis was observed in 4/6 samples, though this effect was also seen in control samples, suggesting possible artifact. Histotripsy treatments with margin extending into adjacent gas-filled bowel do not cause clinically significant damage to the bowel, suggesting that treatments could be performed without displacement techniques. These findings need to be confirmed in an in vivo model.