Clinical outcomes of frameless radiosurgery retreatment for recurrent trigeminal neuralgia
Allan Y. Chen, Michelle B. Chen, Rachel Chou and Conrad T. E. Pappas
Purpose: Stereotactic radiosurgery (SRS) retreatment for trigeminal neuralgia (TGN) patients who failed primary SRS is typically performed with frame-based immobilization. However, the optimal retreatment dose and technique remain unestablished. We report our experience using frameless image-guided radiosurgery (IGRS) retreatment for TGN.
Methods and materials: Between September 2010 and November 2019, 39 TGN patients, including 33 (85%) treated via frameless IGRS, underwent SRS retreatment using a linear accelerator (Linac)-based SRS system. SRS retreatment was delivered via a 6-arc technique to a new retreatment target non-identical to the primary SRS target, determined by the cumulative maximum dose (Dmax) on the trigeminal nerve. Dosimetric variables, including the dorsal root entry zone (DREZ) dose, pons surface dose, and the distance between the primary and retreatment SRS targets were recorded. Clinical outcomes were assessed via patient interviews using the Barrow Neurological Institute (BNI) facial pain and numbness scales. A literature review of Gamma Knife (GK) SRS retreatment for TGN was also conducted.
Results: The median interval between the primary and retreatment SRS was 47 months, with a median follow-up of 19 months. Mean doses for the primary SRS, retreatment SRS and cumulative Dmax were 89.8 Gy (range, 75–90), 60.5 Gy (range, 50–70) and 105.3 Gy (range, 70–116), respectively. Overall, significant pain improvement of 1.9 ± 1.2 points (p < 0.01) on the BNI facial pain scale was achieved. Pain relief was reported in 34 (87%) patients, comprising 9 (23%) complete and 25 (63%) partial responses, occurring at a median of 2.2 months. New or worsening facial numbness occurred in 12 (31%) patients. Facial pain improvement was significantly associated with a history of complete response from the primary SRS (p < 0.05) and no prior invasive procedures (p < 0.05), but was not impacted by atypical pain or multiple sclerosis. Dosimetric analysis showed that concomplete pain response significantly correlated with higher retreatment doses (p < 0.05) and greater distance between the two SRS targets (p < 0.05). Conversely, facial numbness showed no correlation with various dosimetric variables.
Conclusions: Frameless SRS retreatment for TGN is feasible and associated with favorable clinical outcomes. Higher retreatment doses and a greater distance between the primary and retreatment targets on the trigeminal nerve were predictive of successful facial pain relief.
Keywords: trigeminal neuralgia, radiosurgery retreatment, frameless IGRS
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