• Sakina J Attaar, Nitesh V Patel, Eric Hargreaves, Irwin A Keller, and Shabbar F Danish.
• ‡Division of Neurosurgery, Rutgers, Robert Wood Johnson Medical School, New Brunswick, New Jersey; §Department of Radiology, Rutgers, Robert Wood Johnson Medical School, New Brunswick, New Jersey.
• Neurosurgery. 2015 Aug 14.

BackgroundAs magnetic resonance-guided laser-induced thermal therapy (MRgLITT) becomes more accepted, there needs to be an evaluation of the techniques required to achieve accurate laser placement.ObjectiveTo report our experience with frameless stereotaxy and the ability to achieve accurate laser placements. We also evaluate the variables associated with proper placement.MethodsWe performed a retrospective analysis from 3 years of MRgLITT. Demographics and operational parameters, including trajectory length, target alignment error, registration error, and radial error were recorded and compared. Blinded review was used for completeness of ablation.ResultsIn the study, 90 laser placements were evaluated for 72 cases. Trajectory length and target alignment error was 95.3 ± 26.0 mm and 0.7 ± 0.3 mm, respectively. Significant differences existed in registration error between 4 (0.6 ± 0.3 mm) and 5 (0.5 ± 0.2 mm) skull pins (P = .04), but no significant decreases in registration error as additional skull pins were registered. Fifteen laser placements resulted in subtotal ablations. The overall radial error using frameless stereotaxy was 0.9 ± 1.6 mm. In the study, 65% of lasers were exactly on the planned trajectory. Of the 30 that were not, the radial error = 2.6 ± 1.9 mm. Radial error of subtotal laser ablations was 0.5 ± 0.9 (range, 0-2.8 mm) and was not significantly different from 0.8 ± 1.7 (range, 0-7.1 mm) radial error of lasers with total ablations (P = .52). Lasers with radial error >0 mm resulted in an incomplete ablation in 26.7% of cases.ConclusionSkull pin-based frameless stereotaxy for MRgLITT results in consistent accuracy, with the majority of cases resulting in complete ablations. A significant proportion of lasers with RE >0 mm still result in complete ablations.AbbreviationsANOVA, analysis of varianceMRgLITT, magnetic resonance-guided laser-induced thermal therapyPAD, precision aiming deviceRE, radial errorRegE, registration errorSPGR, spoiled gradient echoTAE, target alignment errorTL, trajectory length.

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