3:36 PM Abstract No. 215 Patient-specific needle guidance templates manufactured intraprocedurally for image-guided intervention

Abstract

Multifocal or large tumors can be treated effectively using multiple ablation needles, but it is time consuming and difficult to perform accurately without frequent re-scanning or use of navigation systems. A new targeting method was developed using a custom patient-specific needle guide template, fabricated intraoperatively. In an IACUC approved study, a 78kg pig was studied under general anesthesia. Steel balls (1.5 mm) were implanted into the liver to serve as targets. Fiducial markers were affixed to the abdomen. A custom 150 × 220 mm plastic frame designed to hold two parallel plates was fixed over the abdomen using a rigid mounting arm. The frame and subject underwent CT scan with breath-hold. The targets, fiducial and frame were identified in the images. A preprocedure needle trajectory plan was created for each target, with defined skin entry sites and a path that avoided critical structures. The plan that included all needle paths was converted into a drilling program for an inexpensive numerical-controlled table-top milling machine, and the hole pattern corresponding to the planned trajectories was drilled into two plates. The plates were attached to the frame and needles were passed through the drilled holes toward the targets. After each needle placement, the animal was re-scanned to determine the accuracy of needle placement by determining the distance from needle tip to target. The system was also studied in similar fashion in static phantom experiments. The needle to target error distance for four live animal insertions was 3.2 (standard deviation, 1.8 mm) and ranged between 1.5 and 5.2 mm. The needle delivery technique was feasible for targeting multiple liver locations and facilitated complex oblique paths to the target. The planning step required approximately 5 minutes. The template was manufactured at bedside in 7.5 minutes. Accurate placement of multiple needles using a custom-drilled, patient-specific template (based on a preprocedure CT) is possible and can be performed in the scan room immediately prior to insertion. The system is similar in performance to more complex systems that require tracking.