Abstract No. 331 Feasibility of Mobile C-Arm–Guided Histotripsy: In Vivo Targeting Accuracy and Image Quality

Histotripsy is an emerging focal tumor therapy that utilizes focused ultrasound to mechanically destroy tissue. It is currently guided by diagnostic ultrasound, which is of limited use in cases of acoustic obstructions, large body habitus, or isoechoic tumors. To address these limitations, cone-beam CT (CBCT)-guided histotripsy using a fixed C-arm has been developed. To reduce cost and increase accessibility, mobile C-arm CBCT-guided histotripsy has been proposed and validated in vitro. In this study, we evaluate the targeting accuracy and image quality of the mobile C-arm in an in vivo porcine model. Prior to treatment, the mobile C-arm (CIOS, Siemens) and histotripsy system's robotic arm are registered using a hand-eye calibration approach. Targets (Tg, 1-1.5 cm histotripsy treatments) were created in the liver (n=2) and kidney (n=1) of two ∼50 kg healthy swine. After each Tg creation, a contrast-enhanced mobile CBCT was acquired with a water bath (WB, for acoustic coupling) on the swine's abdomen. Using this image, a larger treatment (Tx, 2-2.5 cm) centered on the target was planned, including a 9 mm offset for aberration correction. The calibrated robotic arm automatically positioned the therapeutic transducer's focal point on each Tg to deliver the Tx (n=3). After each Tx, contrast-enhanced CBCTs with mobile and fixed (Artis zee, Siemens) C-arms were acquired (with WB). Tgs and Txs were segmented using a semi-automated "grow from seeds" method (Slicer 5.0.3). To evaluate targeting accuracy, Euclidean distances between segmentation centroids were measured. To assess Tx detectability and sharpness (observed edge width), respectively, SDNR and the full width half max (FWHM) of Tx edge profile gradients were measured from mobile and fixed CBCTs. Mean Tg and Tx diameters were 18.0 ± 2.5 mm and 37.3 ± 9.8 mm, respectively. Mean centroid offsets between Txs and corresponding Tgs were 1.8 ± 1.0 mm. SDNR was 2.9 ± 0.8 from mobile CBCTs and 1.6 ± 0.8 from fixed. FWHM was 4.7 ± 1.9 mm from mobile CBCTs and 7.3 ± 3.2 mm from fixed. All mobile C-arm-targeted Txs were successful, accurate, and visible in post Tx CBCTs. While the mobile C-arm has a smaller field of view than the fixed, detectability and sharpness of Txs in fixed and mobile CBCTs were comparable. This study suggests a mobile C-arm can provide accurate targeting and adequate image quality for guiding and evaluating histotripsy.