A Comparison of Radiosurgical Planning Techniques for the Treatment of Trigeminal Neuralgia

To survey and analyze the current peer-reviewed literature on physical aspects of radiosurgical treatment of trigeminal neuralgia (TN), and objectively determine the comparative differences between common treatment planning techniques/modalities when variability in computed tomography and magnetic resonance imaging data sets and clinical approaches are minimized.

Example treatment plans were created from 8 distinct planning approaches on a unique computed tomography and magnetic resonance imaging data set. Treatment plan selection comprised Gamma Knife, physical cone, and multileaf collimator-based plans. The prescription was standardized between plans to 85 Gy at the isocenter, as well as the location of the treatment isocenter. Dose distributions were characterized using multiplanar isodose line comparisons, dose line profiles in 2 dimensions, gradient indices, dimensional and volumetric analysis of 50% and 80% isodose coverage, and maximum (0.1 cc) dose to the brainstem as singularly contoured on the unique imaging data set.

Dose coverage, distribution shape, dose line profiles, and gradients differ significantly between Gamma Knife, physical cone, and multileaf collimator-based planning techniques, even when dose prescription, treatment isocenter, and imaging data set/anatomy are identical between treatment plans. Gamma Knife (4 mm collimator) provides the broadest coverage of the trigeminal nerve, most closely approximated by the 5 mm physical cone linear accelerator (LINAC)-based plan. Contrastingly, the smallest cross-sectional coverage in this treatment plan selection was created by the 4 mm LINAC physical cone. All dose distributions were approximately spherical except the 11-arc physical cone LINAC-based plan, which produces a more elongated distribution (broadest adjacent to the brainstem).

The selection of a radiosurgical technique for TN should be weighed in the context of differences in dose distributions between treatment techniques, as demonstrated by the plans analyzed in this study. It cannot be assumed that all TN radiosurgical techniques produce the same dose distribution, either to the trigeminal nerve or adjacent normal tissues. Differences between planning techniques may be amplified in real clinical scenarios with differences in clinical approach and anatomy.