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DOI: 10.1055/s-0035-1546581
Tumor Volume Threshold for Achieving Improved Conformity Index in VMAT and Gamma Knife Stereotactic Radiosurgery for Vestibular Schwannoma
Background and Purpose: Recent advances in multileaf collimator field shaping technology and inverse planning software have resulted in highly conformal LINAC-based stereotactic radiosurgery (SRS) plans with minimal dose to critical structures. This modeling study compares Gamma Knife (GK) and LINAC SRS for vestibular schwannoma.
Materials and Methods: A total of 76 treatment plans from 19 patients with vestibular schwannoma were planned using GK forward planning and volumetric arc therapy (VMAT) inverse planning software. VMAT plans were generated with 1 coplanar and 3 of 5noncoplanar arcs. Dose to normal structures and beam on time (dose rate 600 MU/min) were compared using Kruskal–Wallis and Dunn post hoc test.
Results: Median tumor volume was 1.2cc (range, 0.1–4.8cc). A peripheral tumor dose of 12 Gy was prescribed. Tumor coverage was > 99.8% for all plans. VMAT plans had lower target maximum and mean dose, as well as decreased beam-on time, compared with GK plans (p < 0.0001). Conformity index in VMAT 3 and 5 arc plans was superior to that of GK plans for targets > 0.3 cc (p = 0.011). Similar dose to cochlea, normal brain tissue, and brain stem were observed.
Conclusion: VMAT should be considered as a safe, alternative modality to GK for vestibular schwannoma SRS treatment, especially for tumors larger than 0.3cc.