Dosimetric Comparison of Brain Sparing Between HyperArc and GammaKnife for Single to Triple Brain Metastases

Background/Aim: A novel linac-bases radiosurgery (SRS) system, HyperArc, applied to the non-coplanar volume-modulated arc therapy (VMAT) technique, was developed and released in clinical practice. The aim of the study was to evaluate the dosimetric performance of brain sparing in single-target to three-target cases, for two types of SRS systems: GammaKnife and HyperArc.

Patients and Methods: A total of 83 patients treated with GammaKnife SRS (35 with single, 24 with double, and 24 with triple metastases) were retrospectively analyzed. Treatment plans were recalculated using HyperArc. Dosimetric parameters, including conformity index (CI), gradient index (GI), and brain volume receiving 2-20 Gy (V₂-V₂₀), were compared between the two systems.

Results: No significant difference in D₉₉ of the planning target volume (PTV) was observed between GammaKnife and HyperArc. HyperArc exhibited superior CI₁₀₀, with values approaching 1.0. V₄-V₂₀ for the whole brain minus PTV were significantly lower for HyperArc than GammaKnife. In single-target cases, GI was significantly lower for HyperArc, while in triple-target cases, it was higher. V₁₂ volumes for HyperArc were comparable to those for GammaKnife, even in cases with volumes <1.0 cm³.

Conclusion: HyperArc demonstrated dosimetric performance comparable to or better than GammaKnife in brain sparing for single-to-triple metastases. These findings support HyperArc as an effective alternative for SRS planning.