Accuracy and precision of targeting using frameless stereotactic system in deep brain stimulator implantation surgery

Objectives: To assess the accuracy of targeting using NexFrame frameless targeting system during deep brain stimulation (DBS) surgery. Materials and Methods: Fifty DBS leads were implanted in 33 patients using the NexFrame (Medtronic, Minneapolis, MN) targeting system. Postoperative thin cut CT scans were used for lead localization. X, Y, Z coordinates of the tip of the lead were calculated and compared with the intended target coordinates to assess the targeting error. Comparative frame-based data set was obtained from randomly selected 33 patients during the same period that underwent 65 lead placements using Leksell stereotactic frame. Euclidean vector was calculated for directional error. Multivariate analysis of variance was used to compare the accuracy between two systems. Results: The mean error of targeting using frameless system in medio-lateral plane was 1.4 mm (SD ± 1.3), in antero-posterior plane was 0.9 mm (SD ± 1.0) and in supero-inferior plane Z was 1.0 mm (SD ± 0.9). The mean error of targeting using frame-based system in medio-lateral plane was 1.0 mm (SD ± 0.7), in antero-posterior plane was 0.9 mm (SD ± 0.5) and in supero-inferior plane Z was 0.7 mm (SD ± 0.6). The error in targeting was significantly more (P = 0.03) in the medio-lateral plane using the frameless system as compared to the frame-based system. Mean targeting error in the Euclidean directional vector using frameless system was 2.2 (SD ± 1.6) and using frame-based system was 1.7 (SD ± 0.6) (P = 0.07). There was significantly more error in the first 25 leads placed using the frameless system than the second 25 leads (P = 0.0015). Conclusion: The targeting accuracy of the frameless system was lower as compared to frame-based system in the medio-lateral direction. Standard deviations (SDs) were higher using frameless system as compared to the frame-based system indicating lower accuracy of this system. Error in targeting should be considered while using frameless stereotactic system for DBS implantation surgery.