Higher LINAC SRS dose rate was linked to longer pain control in trigeminal neuralgia

KEY POINTS

• The single-centre retrospective analysis included 113 first LINAC-SRS treatments for classical trigeminal neuralgia after 21 exclusions. Mean age was 66.2 years, and 29/113 patients (25.6%) had multiple sclerosis.
• Every patient received the same nominal prescription: 40 Gy to the 50% isodose line with an 80-Gy maximum, targeting the proximal trigeminal nerve root. Treatment was delivered at either 800 MU/min (~4 Gy/min) or 2400 MU/min (~12 Gy/min).
• The low-dose-rate group comprised 71 treatments and the high-dose-rate group 42. One-year treatment failure, defined as BNI pain class ≥IV, was 42.7% at 800 MU/min versus 14.4% at 2400 MU/min; at five years, failure rates were 55.1% versus 30.0%.
• Kaplan–Meier analysis showed longer pain control with the higher dose rate (p=0.002). In multivariable Cox analysis, lower dose rate was the only significant predictor of failure (HR 3.43, 95% CI 1.33–8.84; p=0.011).
• Clinically bothersome facial numbness was almost identical: 4.8% at 2400 MU/min versus 5.6% at 800 MU/min (p=0.771), suggesting that the apparent gain in pain control was not accompanied by an obvious increase in sensory toxicity.
• Modeled biologically effective dose was significantly higher in the 2400-MU/min cohort, consistent with less intrafraction repair during faster dose delivery. Detailed dosimetric analyses did not identify obvious target or OAR differences sufficient to explain the clinical result.
• The comparison remains strongly confounded by treatment era: the 800-MU/min cohort used an older Brainlab Novalis platform, whereas later patients received 2400-MU/min 10-MV FFF treatment on a Varian Edge. Importantly, when failure was redefined as BNI IIIb or worse rather than BNI IV, the difference between dose-rate cohorts disappeared.

CLINICAL TAKEAWAY

SOURCE

Radiotherapy and Oncology