Evaluation of Dosimetric and Treatment Parameter Differences between Hyperarc and Non-Coplanar VMAT Treatment Planning for Intracranial FSRT
Abstract
Purpose
This study evaluates the dosimetric impact and treatment delivery parameter differences between HyperArc (HA) volumetric modulated arc therapy (VMAT) and non-coplanar VMAT treatment planning for intracranial fractionated stereotactic radiotherapy (FSRT).
Methods
HA planning integrates an SRS Normal Tissue Objective (SRS NTO) with Automatic-Lower Dose Objective (ALDO) to promote higher prescription isodose levels to the target, consistent coverage, steeper dose gradients, and more rapid dose fall-off during optimization. To assess its performance, paired HA VMAT and non-coplanar VMAT plans were generated using the Varian Eclipse treatment planning system (TPS). Select organ-at-risk (OAR) structures were manually contoured to ensure anatomical consistency between phantom and patient geometries. Gross tumor volume (GTV) and planning target volume (PTV) coverage, OAR sparing, and treatment delivery parameters were compared between plans.
Results
HA planning enabled dose escalation to the GTV and PTV while maintaining OAR doses comparable to those of the non-coplanar VMAT plan. Percentage differences in PTV coverage between HA and non-coplanar plans were 8.22% at V105% and 1.01% at V100%, with minimal differences observed at V95% and V90%. A 3.2cGy difference was observed at D95%. At D1%, dose differences for the optic nerves, optic chiasm, spinal cord, and healthy brain were 35.3cGy, 12.1cGy, 0.4cGy, and 43.8cGy, respectively. Both plans utilized four half arcs; however, collimator angles differed substantially. The HA plan employed collimator angles of 78.0°, 117.0°, 21.0°, and 15.0°, compared with 335.0°, 355.0°, 40.0°, and 25.0° for the non-coplanar plan. Couch kick angles were similar between plans. The HA plan required fewer monitor units (2381 vs. 2595).
Conclusion
HA VMAT treatment planning, incorporating ALDO and the SRS NTO, provides improved dose conformity, higher target dose, and reduced treatment delivery requirements while maintaining OAR sparing comparable to conventional non-coplanar VMAT planning for intracranial FSRT.