Room: Room 209
Purpose: HyperArc was recently developed to streamline the planning and delivery of intracranial SRS. We compared the plan quality of HyperArc plans with the conventional VMAT plans.
Methods: Ten challenging brain SRS cases with 2-6 metastases were retrospectively selected. The original VMAT plans were performed using Eclipse V13.7 for Truebeam to deliver 18-32.4 Gy in one or three fractions. Depending on the target locations, 3-5 non-coplanar arcs were used. Five cases were planned with one isocenter, four with two isocenters, and one with three isocenters. Each case was replanned with a single-isocenter HyperArc technique using a test version of Eclipse V15.5.11. The HyperArc plans used one full arc with couch at 0Â° and three half non-coplanar arcs with couch at 45Â°, 315Â°, and 90Â° (or 270Â°). The HyperArc plans were normalized to match the PTV coverage in the clinical plans. The Truebeam VMAT plans and HyperArc plans were compared using dosimetric endpoints, homogeneity index (HI), conformity index (CI), gradient index (GI) and total MU. Paired t-tests were performed with a significance level of 0.05.
Results: HyperArc plans achieved higher HI (1.29Â±0.14 vs. 1.22Â±0.09, p=0.011), similar CI (1.14Â±0.32 vs. 1.14Â±0.35, p=0.999), similar GI (15.1Â±21.0 vs. 14.6Â±18.8, p=0.609), and similar MU (5175Â±1837 vs. 6683Â±3816, p=0.174) compared to the Truebeam VMAT plans. Doses to the brain (V10Gy: 24.3Â±11.8 vs. 31.9Â±14.6 cc, p=0.006) and brainstem (D0.1cc: 3.7Â±5.8 vs. 4.7 Â± 5.8 Gy, p=0.006) were significantly reduced in the HyperArc plans compared to the VMAT plans. Doses to the left eye (D0.1cc: 1.0Â±0.5 vs. 0.9 Â± 0.3 Gy, p=0.545) and right eye (D0.1cc: 0.8Â±0.4 vs. 0.8 Â± 0.2 Gy, p=0.751) were similar between the two plans.
Conclusion: For challenging multiple brain metastases SRS cases, HyperArc planning reduced dose to brain and brainstem compared to conventional VMAT plans while maintaining target dose coverage.