Design and Validation of a Steerable Port Delivery Cannula System for Laser Interstitial Thermal Therapy

Abstract

MRI (Magnetic Resonance Imaging) guided laser interstitial thermal therapy (LITT) is a procedure used for treating glioblastomas and epilepsy lesions in the brain. Current methods for placing LITT ablation probes use straight trajectories. This limits the treatment area, necessitating multiple passes of straight trajectories or risking untreated tumor margins. This work presents a port delivery cannula system (PDCS) to be integrated within existing surgical workflows of LITT, providing off-axis navigation to areas otherwise deemed inaccessible. The design of the PDCS is centered around a two-tube, Nitinol active cannula system, which delivers, places, and retracts a flexible, thermoplastic port along curved trajectories. We present the design of the PDCS system and validate it in free-space, phantom models, and ovine brain trials, with a specific focus on evaluating key parameters of port material characteristics. Eight commercial, biocompatible ports and five custom ports created using additive manufacturing were investigated. Results illustrate that ideal port characteristics include durometers between 85A-95A, a low coefficient of friction, and a wall thickness of approximately 20% of the overall port diameter. Our results also demonstrate that the PDCS system can achieve accuracies under 1mm in phantom models and 2mm in ovine tissue.