ESTRO 2025 - Abstract Book

S4313

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

Keywords: MSCC, Simulation-free, oART

316

Digital Poster Dosimetric comparison between co-planar VMAT and HyperArc in treating skull base meningioma with fractionated stereotactic radiotherapy Tin Long Wong Department of Clinical Oncology, Pamela Youde Nethersole Eastern Hospital, Hong Kong, Hong Kong Purpose/Objective: Meningioma is a common CNS tumour which could be treated by volumetric-modulated arc therapy (VMAT). Nonetheless, delivering radiotherapy to skull base meningiomas (SBM) may pose challenges in achieving optimal tumour dose coverage due to dosage limitations imposed by adjacent critical structures, including the brainstem, optic chiasm, and optic nerves. Furthermore, irradiation directed at the hippocampus, temporal lobes, and normal brain regions raises concerns regarding potential cognitive impairments, given the notable survival rates. However, protecting the hippocampus and normal brain tissue while giving an adequate dose to the meningioma could be difficult when using co-planar VMAT. HyperArc is an advanced technique using automated non-coplanar arcs to treat single or multiple intracranial lesions. This study aims to investigate the dosimetric benefit of Hyperarc by comparing VMAT and HyperArc when treating SBM. Material/Methods: Fifteen patients with grade I skull base meningioma (SBM) treated by a 54Gy/30fractions radiotherapy were selected and replanned using VMAT and HyperArc. The dose coverage (V100%, D98%, D2% and Dmean), Paddick's conformity index (PCI), homogeneity index (HI) and gradient index (GI) of the PTV are compared. For the OARs, the Dmax of brainstem, spinal cord, optic nerves, optic chiasm, lenses, and eyeballs are compared. V20Gy and Dmean of temporal lobes, V55Gy, Dmean and D40% of the hippocampus and V10Gy, V20Gy, V30Gy and Dmean of the normal brain tissue (Brain - PTV) are chosen for comparison respectively. Moreover, to investigate the treatment efficiency, the beam-on time is estimated by Mobius3D software and compared. Results: HyperArc plans have a significantly better PCI (0.72 vs 0.80) and GI (4.78 vs 3.09) than VMAT plans. However, HyperArc generally produces plans with greater D2% (55.1Gy vs 55.6Gy) and hence a poorer HI (0.115 vs 0.13). The V100% of PTV is insignificant between VMAT and HyperArc (84.3% vs 86.9% p=0.304). With regards to OARs, HyperArc gave a significantly higher Dmax to the spinal cord (+3.36Gy) but significantly lower V20Gy in the ipsilateral (-20.6%) and contralateral (-21.68%) temporal lobe, significantly lower D40% (-12.7Gy) and Dmean (- 11.74Gy) in the contralateral hippocampus. Hyperarc also significantly reduced V20Gy (-7.05%) and V30Gy (-2.07%) of the normal brain tissue. However, the beam-on time of HyperArc is significantly longer than VMAT (+74s). Conclusion: HyperArc provides a highly conformal plan with a steep dose gradient, and better dose sparing at temporal lobes, hippocampus and normal brain tissue but with increased hotspots and longer treatment time. In short, HyperArc is a feasible alternative to VMAT in treating SBM.

Keywords: HyperArc, Skull Base Meningioma, VMAT

References: 1. Fathi A-R, Roelcke U. Meningioma. Current neurology and neuroscience reports. 2013;13:1-8. 2. Moraes FY, Chung C. Radiation for skull base meningiomas: review of the literature on the approach to radiotherapy. Chin Clin Oncol. 2017;6(Suppl 1):S3.