Coplanar versus non-coplanar volumetric modulated arc therapy for hippocampal avoidance whole brain radiotherapy using Monte Carlo-based planning system.

This retrospective study evaluates the dosimetric performance of coplanar versus non-coplanar volumetric modulated arc therapy (VMAT) for hippocampal avoidance whole-brain radiotherapy (HA-WBRT) using the Monaco treatment planning system. Ten patients were replanned using four techniques: three coplanar configurations with two, three, and four arcs, and one plan with both coplanar and non-coplanar arcs. A prescription of 30 Gy in 10 fractions was delivered to the planning target volume (PTV). Increasing the number of coplanar arcs improved target coverage and homogeneity, with the four-arc coplanar plan achieving PTV coverage, conformity, and homogeneity comparable to the non-coplanar approach. All techniques met protocol constraints for hippocampal and organ-at-risk doses, although non-coplanar VMAT produced the lowest absolute hippocampal doses. Non-coplanar plans required higher monitor units and longer treatment times. Four-arc coplanar VMAT demonstrated comparable dosimetric performance with improved delivery efficiency, supporting its use as a practical alternative in settings where non-coplanar delivery is limited.