SU-D-BRB-05: Gamma Knife and Volumetric Modulated Arc Therapy Stereotactic Radiosurgery Have Equivalent Plan Quality and OAR Sparing for Pituitary Adenomas and Vestibular Schwannomas

Abstract

Purpose: To compare the plan quality and organs at risk (OAR) sparing of volumetric modulated art therapy (VMAT) and Gamma Knife for stereotactic radiosurgery (SRS) of pituitary adenomas and vestibular schwannomas (VS). Methods: VMAT radiosurgery plans (SmartArc) were made using Pinnacle’s (version 9.10, Phillips) new Auto-Plan tool for eight vestibular schwannoma (VS) and eight pituitary adenoma patients previously treated with Gamma Knife Perfexion (GK) system. VMAT plans were made with three non-coplanar arcs using 3 angles, 6MV, FFF mode at 1400 MU per min dose rate and millennium HD MLC. All plans were normalized to deliver prescription dose (Rx) to at least 99.5 percent of the target volume. Results: For pituitary cases (1.07 – 20.71cc), respectively for GK and VMAT plans, mean conformity index (CI) was 1.62 ± 0.23 Gy and 1.51 ± 0.21 Gy (p = 0.05); mean gradient index (GI) was 2.76 ± 0.14 and 3.15 ± 0.43 Gy (p < 0.05); mean brainstem maximum dose was 9.13 ± 3.50 Gy and 7.31 ± 2.01 Gy (p < 0.05); mean optic nerve maximum dose was 9.66 ± 1.0 Gy and 7.67 ± 2.58 Gy (p < 0.05); and mean treatment time of 68 min and 4 min. For VS (0.47 – 5.26cc), respectively for GK and VMAT plans, CI was 1.39 ± 0.23 Gy and 1.57 ± 0.28 Gy (p < 0.05); GI was 3.71 ± 1.83 and 3.60 ± 0.84 Gy (p = 0.82); brainstem maximum dose was 11.67 ± 4.56 Gy and 12.22 ± 4.56 Gy (p = 0.12), cochlea mean dose was 7.31 ± 2.7 Gy and 6.75 ± 3.88 Gy (p = 0.52); and mean treatment time of 40 min and 4 min. Conclusion: VMAT plan quality and OAR sparing were comparable to GK plans with a shorter treatment time. Samuel Chao is a member of Varian Speakers Bureau, Gennady Neyman is a consultant for Elekta Instrument A/B