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Published on: May 26, 2019
Dose rate matters: comparative outcomes of high and low dose rate LINAC stereotactic radiosurgery in trigeminal
Sara A Alaqel1, Matthew J Frick2, Wesley Kelman3
1University of Calgary, Department of Clinical Neuroscience, Division of Neurosurgery, Canada.
Purpose:
To evaluate the impact of dose rate on clinical outcomes in patients undergoing linear accelerator stereotactic radiosurgery (linac SRS) for trigeminal neuralgia (TN).
Methods:
We analyzed outcomes of 134 frame-based linac SRS treatments for TN performed at our institution. Twenty-one treatments were excluded for not meeting the inclusion criteria. Each treatment was performed by the same clinical team and consisted of 40 Gy prescribed to the 50 % isodose line with maximum point dose of 80 Gy, targeting the proximal trigeminal nerve root. All included treatments were delivered using a dose rate of 800 monitor units (MU) per minute or 2400 MU⋅min-1, corresponding to approximately 4 Gy⋅min-1 and 12 Gy⋅min-1. Clinical outcomes were assessed using the Barrow Neurological Institute pain intensity and facial numbness scales. Both univariate and multivariate analysis of patient demographics on clinical outcomes were performed using age, comorbidity with multiple sclerosis, time between diagnosis and treatment, previous procedures, and dose rate. Biologically effective dose (BED) was calculated and compared between each dose rate cohort. Furthermore, a comprehensive review of the dosimetric consistency of all plans was performed to assess potential effects on clinical outcomes.
Results:
Kaplan-Meier analysis and log-rank statistics indicated a statistically significant improvement in pain relief for patients treated with the higher dose rate (p = 0.002). Cox proportional hazards modelling identified dose rate as the only statistically significant hazard, with a hazard ratio of 3.43 (95 % CI = [1.33, 8.84], p = 0.011). All dosimetric consistency tests confirmed comparable treatment delivery across and within cohorts, and a Mann-Whitney U test analysis of the BED between dose rate groups confirmed a statistically significantly higher BED in the 2400 MU⋅min-1 group (p < 0.05).
Conclusions:
Higher dose rates using cone and frame-based linac-SRS for TN are associated with improved patient outcomes.
