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A Comparison Between Flattening-Filter-Free and Flattenedmodes for LINAC-Based Trigeminal Neuralgia SRS

D Zheng

D Zheng*, S Wang, C Zhang, Q Fan, V Verma, R Ma, S Zhou, University of Nebraska Medical Center, Omaha, NE


SU-I-GPD-T-628 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To compare dosimetry, clinical outcome, and delivery efficiency between modern flattening-filter-free(FFF) and conventional flattened modes for LINAC-based trigeminal neuralgia(TN) SRS.

Methods: Twenty patients treated with 6XFFF beams on a Varian TrueBeamStx and twenty with 6X on a BrainLab Novalis were analyzed. Both cohorts used identical non-coplanar arc arrangements, SRS frame localization, and verified by CBCT (TrueBeamStx) or Exac Trac (Novalis). Prescription was 90Gy maximum dose, with 90% isodoseline bisecting the nerve using 5 or 6mm SRS cones depending on the nerve thickness. Dosimetry data were compared using V12Gy to non-nerve brain tissue, V10Gy to brainstem, and maximum brainstem dose. Clinical outcome was compared using pain relief and toxicity recorded in follow-up notes. Delivery efficiency was compared using recorded treatment time from R&V. Mann-Whitney-U tests were used for statistical evaluation.

Results: A slightly lower normal tissue V12Gy was observed for 6XFFF beam. Among the 30 patients treated with a 6mm cone, average V12Gy was 1.42cc (range:1.22-1.70) for 6XFFF vs. 1.63cc (range:1.41-1.86) for 6X (p=0.01). Brainstem dose was correlated with isocenter-to-brainstem distance. With a 21-month median post-SRS duration (range:6-32) for the 6XFFF patients, 17 had complete response, 1 relapsed, 1 had persistent pain, and 1 was lost to followup. With a 48-month median duration (range:39-71) for the 6X patients, 10 had complete response, 3 relapsed, 1 had persistent pain, and 6 were lost after the first followup. Facial numbness was recorded for 6(out of 19) 6XFFF and 4(out of 14) 6X patients. A 33% beam-on and 8% overall-treatment time reduction was achieved using 6XFFF vs. 6X.

Conclusion: In a 40-patient series, 6XFFF achieved similar dosimetry and clinical outcome as 6X beams in LINAC-based SRS for TN, with slightly lower normal tissue V12Gy. FFF modes offered by modern LINACs appear to be effective for such treatments with improved delivery efficiency.

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