Accuracy of laser placement with frameless stereotaxy in magnetic resonance-guided laser-induced thermal therapy

BACKGROUND: As 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. OBJECTIVE: To report our experience with frameless stereotaxy and the ability to achieve accurate laser placements. We also evaluate the variables associated with proper placement. METHODS: We 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. RESULTS: In 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. CONCLUSION: Skull 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.