Scientific Abstracts: Thoracic, Renal, and Bone
Objective: Lung cryoablation has been limited to percutaneous cryoprobes. Recently, a prototype flexible cryoprobe that can be delivered through a bronchoscope or steerable guiding sheath was developed for endobronchial or transbronchial cryoablation. In this study, a transbronchial flexible cryoprobe was evaluated and compared to a transthoracic percutaneous cryoprobe in swine lung.
Methods: All procedures were approved by the Institutional Animal Care and Use Committee. Cryoablation was performed under general anesthesia (n=4 swine, two lung ablations per swine) using a prototype flexible endobronchial cryoprobe (1.9mm) delivered transbronchial (n=6 ablations), or a percutaneous commercial cryoprobe delivered transthoracic (n=2 ablations) (IceForce 2.1 CX, 2.1mm, 14G) (Galil, BTG, Boston scientific). Freezing and active thawing were accomplished with argon and helium, respectively, for the endobronchial probe or argon freezing and electrical heating for the rigid probe. The endobronchial probe was navigated under image guidance to central and lower lobes using a 6.5 F or 7 F steerable sheath (Destino Twist, Oscor, FL, USA). The percutaneous probe was delivered directly through the thoracic wall. Image guidance during both approaches was performed with fluoroscopy, cone beam CT [CBCT], and preplanned delivery pathways to enable augmented fluoroscopy (OncoSuite, Philips). All cryoablation was performed using a triple-freeze lung protocol: 3 min freeze, 3 min passive thaw, 7 min freeze, 3 min passive thaw, 10 min freeze, 2 min passive thaw, and 1 min active thaw. Following each freeze/thaw cycle, a CBCT was acquired. Cryoablation zones were identified and measured on CBCT along and orthogonal to the probe axis, and cryoablation volumes were calculated using an ellipsoid shape model. Following euthanasia, ablation sites were explanted and sectioned perpendicular to the axis of the probe for pathology.
Results: The endobronchial cryoprobe was successfully navigated to each treatment site with a steerable sheath (6/6). At the target site, the active component of the cryoprobe was advanced 32-43mm from the steerable sheath and a complete triple-freeze-thaw cryoablation was performed. The cryoablation zones of 2/2 percutaneous rigid and 5/6 endobronchial flexible cryoprobe ablations were visualized on CBCT. For the cryoablation zone that could not be detected on CBCT, the cryoprobe was delivered in a 10 mm airway, with minimal coaptation between the probe and bronchial wall. Based on post-treatment CBCT, the cryoablation zones measured 56 (12)ml for centrally delivered endobronchial cryoprobe (n=2), 72 (15)ml for peripherally delivered endobronchial cryoprobe (n=3) and 80 (16) ml for percutaneously delivered cryoprobes (n=2). Pneumothorax developed after withdrawal of the probe in 1/6 transbronchial cryoablation cases due to a visceral pleural puncture. Pneumothorax occurred in both transthoracic cryoablation cases (2/2) prior to or during the first freeze cycle. Cryoablation zones were noted on gross pathology and correlated with CBCT images of the cryoablation zone.
Conclusions: In addition to transthoracic cryoablation, transbronchial cryoablation with an endobronchial flexible cryoprobe was shown to be feasible in a swine model. The endobronchial cryoprobe could be delivered through a steerable guiding sheath, and all cryoablation zones were imageable by CBCT with correlative gross pathology. Asymmetric ablation zones may reflect the effects of convective heating due to vascular flow or insulation by air if the probe is not in direct contact with bronchial walls. Design or technique modifications could lead to an improvement in device performance.