A Study of Six-Dimensional Intrafractional Shifts During Frameless Image-Guided Radiosurgery and Pain Outcome for Trigeminal Neuralgia

Abstract

Precision targeting is essential to successful stereotactic radiosurgery (SRS) for trigeminal neuralgia (TGN). We investigate the impact of intra-fractional 6-dimensional shifts during frameless image-guided stereotactic radiosurgery (IGRS) on pain relief outcome for TGN patients. A total of 41 sets of intra-fractional shifts from 35 patients with idiopathic TGN treated by a dedicated Linac-based radiosurgery unit from 2009 to 2013 were retrospectively studied. All patients were immobilized by facemask and received 90 Gy point dose via a 4 mm cone from an average of 6 non-coplanar arcs to the affected trigeminal nerve. The in-room kV X-ray imaging system with 6-degree of freedom robotic couch was utilized for image-guided positioning corrections. During each frameless IGRS, translational shifts in lateral, longitudinal and vertical directions, as well as rotational shifts in pitch, roll and yaw were conducted at each couch angle. These 6-dimentional shifts and the average calculated distance derived from translational shifts were analyzed and correlated with clinical pain outcome. Clinical pain outcome was assessed by patient interviews according the 5-point Barrow Neurological Institute (BNI) pain scale. Student’s t test was used to detect significance between values. The absolute mean lateral, longitudinal and vertical translational were 0.46 ± 0.15, 0.36 ± 0.16 and 0.21 ± 0.08 mm, respectively. The absolute mean pitch, roll and yaw rotational shifts were 0.33 ± 0.24, 0.18 ± 0.09 and 0.27 ± 0.15 degrees, respectively. For patients with less than 2 points of pain relief, the absolute mean lateral, longitudinal and vertical translational shifts were 0.09 ± 0.01, 0.14 ± 0.01 and 0.09 ± 0.01 mm, respectively. The average calculated distance shift for patients with less than 2 points of pain relief was 0.23 ± 0.01 mm. The average absolute pitch, roll and yaw rotational shifts for these patients were 0.15 ± 0.01, 0.10 ± 0.00 and 0.09 ± 0.01 degrees, respectively. For patients with at least 2 points of pain relief, the average absolute lateral, longitudinal and vertical translational shifts were 0.12 ± 0.00, 0.16 ± 0.01 and 0.09 ± 0.00 mm, respectively. The average calculated distance shift for these patients was 0.26 ± 0.01 mm. The average absolute pitch, roll and yaw rotational shifts for these patients were 0.14 ± 0.01, 0.10 ± 0.00 and 0.13 ± 0.00 degrees, respectively. The two patient groups demonstrate no statistically significant difference in the translational or rotational intra-fractional shifts. Our analysis revealed no correlation between pain relief outcome and the amount of intra-fractional shift in all six dimensions during frameless IGRS. Our results indicate the less than 0.5 mm nominal mechanical deviation during frameless IGRS does not impact on TGN pain outcome.