Patient-specific templates for image-guided intervention-a phantom study

Purpose: To evaluate the in vitro accuracy of a new device and method for simultaneous stereotactic CT-guided punctures. Material and methods: 240 needle paths were planned in 1 mm, 1.5 mm and 3 mm slice thickness with a custom-designed software. The data were transferred to a three-axis tabletop CNC machine that then drilled the hole pattern for the needles into square plastic plates. Kirschner wires were slid through the holes of the two parallel fixed plates to aim at the chosen targets inside the phantom. The accuracy was calculated by taking control CTs and measuring the Euclidean distance and the normal distance between the wire and the entry and target point. Results: The mean Euclidean distance of the wire tip to the target for the 1 mm, 1.5mm and 3 mm slice thickness were 2.5 mm (SD +/- 0.64), 2.71mm (SD +/- 0.78) and 2.8 mm (SD +/- 1.0). The mean normal distance was 1.42 mm (SD +/- 0.65), 1.43mm (SD +/- 0.75) and 1.9 mm (SD +/- 1.1), respectively. Conclusion: The system yields satisfactory accuracy comparable to other image-guided intervention systems. Involuntary movements of the patient need to be taken into account in a clinical setting.