Dosimetric Evaluations of HyperArc and RapidArc in Stereotactic Radiosurgery for a Single Brain Metastasis

Purpose: This study assessed and compared the dosimetric performance of HyperArc and RapidArc in stereotactic radiosurgery (SRS) for a single brain metastasis.Methods: Twenty patients with intracranial brain metastases, each presenting a distinct target volume, were retrospectively selected.Subsequently, volumetric modulated arc therapy (VMAT) plans were designed using RapidArc (VMAT RA ) and HyperArc (VMAT HA ) for each patient.For planning comparisons, dose-volumetric histogram (DVH) parameters for planning target volumes (PTVs) and normal brain regions were computed across all VMAT plans.Subsequently, their total monitor units (MUs), total beam-on times, and modulation complexity scores for the VMAT (MCS v ) were compared.A statistical test was used to evaluate the dosimetric disparities in the DVH parameters, total MUs, total beam-on times, and MCS v between the VMAT HA and VMAT RA plans.Results: For the PTVs, VMAT HA presented a higher homogeneity index (HI) than VMAT RA .Moreover, VMAT HA presented significantly smaller gradient index (GI) values (P<0.001)than VMAT RA .Thus, VMAT HA demonstrated better performance in the DVH parameters for the PTV than VMAT RA .For normal brain tissues, VMAT HA presented lower volume receiving 50% of the prescription dose and V 2Gy to the normal brain tissues than VMAT RA (P<0.0001).While the total MUs required for VMAT HA was significantly higher than those for VMAT RA , the total beam-on time for VMAT HA was superior to that for VMAT RA .Conclusions: Thus, VMAT HA exhibited superior performance in achieving rapid dose fall-offs (as indicated by the GI) and a higher HI at the PT V compared to VMAT RA in brain SRS.This advancement positions HyperArc as a significant development in the field of radiation therapy, offering optimized treatment outcomes for brain SRS.