Application of volumetric modulated arc therapy (VMAT) for craniospinal irradiation: Dosimetric analysis and clinical implementation

Craniospinal irradiation (CSI) is crucial for treating central nervous system malignancies like medulloblastoma and high-risk brain tumors with meningeal spread potential. Traditional 3D-conformal radiotherapy (3D-CRT) requires multiple field junctions, increasing the risks of dose inhomogeneity and unnecessary exposure to healthy tissues. This study investigates the use of VMAT on an Elekta Synergy linear accelerator with 160 leaf Agility multi-leaf collimator at the Hue Central Hospital, Vietnam. Five pediatric patients were treated using VMAT with a prescribed dose of 23.4 Gy in 13 fractions. Immobilization was achieved using vacuum bags and thermoplastic masks in a supine position. Planning CT scans were performed with 3-mm slice thickness, and treatment plans were created using the Monaco treatment planning system, v6.1.4.0. VMAT plans incorporated two isocenters with overlapping arcs to ensure comprehensive craniospinal coverage. Key parameters, including conformity index (CI), homogeneity index (HI), monitor units (MU), and dose to organs-at-risk (OARs), were analyzed. Mechanical and positional uncertainties, including simulated f3 mm patient shifts, were also evaluated. The planning target volume (PTV) achieved exceptional coverage, with V95 % averaging 99.27 f 0.52 % and hotspot volumes (V107 % and V110 %) minimized to 1.96 f 0.39 % and 0.05 f 0.07 %, respectively. The CI and HI averaged 0.93 f 0.02 and 1.06 f 0.01, indicating outstanding plan quality and dose uniformity. OAR doses, including those for critical structures like the lenses, lungs, heart, and kidneys, adhered to planning constraints, minimizing potential long-term side effects. Treatment efficiency was demonstrated with an average MU of 1197.56 f 88.49, showcasing the practicality of the approach. This study demonstrates the successful implementation of VMAT for CSI on the Elekta Synergy system. The results highlight excellent PTV coverage, minimal hotspot volumes, and high plan quality with optimal conformity and homogeneity indices. Doses to OARs remained within safe limits, minimizing potential adverse effects.