J Neurol Surg B Skull Base 2015; 76 - A115
DOI: 10.1055/s-0035-1546581

Tumor Volume Threshold for Achieving Improved Conformity Index in VMAT and Gamma Knife Stereotactic Radiosurgery for Vestibular Schwannoma

Hyun Kim 1, Peter Potrebko 1, Amanda Rivera 1, Haisong Liu 1, Harriet B. Eldredge-Hindy 1, Vickie Gunn 1, Maria Werner-Wasik 1, David W. Andrews 2, James J. Evans 2, Christopher J. Farrell 2, Kevin Judy 2, Wenyin Shi 1
  • 1Department of Radiation Oncology, Sidney Kimmel Medical College at Thomas Jefferson University, Philadelphia, Pennsylvania, United States
  • 2Department of Neurosurgery, Sidney Kimmel Medical College at Thomas Jefferson University, Philadelphia, Pennsylvania, United States

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.