Optimization and clinical validation of dosimetric leaf gap settings in Mobius3D for patient-specific quality assurance

Background: Independent dose verification is essential for quality assurance in radiotherapy. The accuracy of Mobius3D depends on proper dosimetric leaf gap (DLG) settings. This study aimed to optimise and validate DLG parameters for different photon energies to improve clinical implementation. Materials and methods: The study was conducted at the Department of Oncology and Radiotherapy, University Clinical Center in Gdansk, using four Varian TrueBeam linacs [high-definition multileaf collimator (HD-MLC) and Millennium MLC]. Verification plans were recalculated in Mobius3D with DLG values of −1 mm, 0 mm, and +1 mm, and linear regression was used to determine optimal DLGs. Subsequently, 38 clinical plans [volumetric modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT)] were delivered to a Mobius Verification Phantom™ for ion-chamber measurements. Measured doses were compared with Eclipse treatment planning system (TPS) and Mobius3D calculations. Finally, 87 patient plans were recalculated using the optimal DLGs and correction factors using different configurations: default Autodetection and stereotactic radiosurgery (SRS) mode with a 1 mm grid. Agreement was assessed via gamma analysis and dose–volume histogram (DVH) parameters. Results: Phantom measurements showed a linear relationship between DLG and dose differences. Optimal DLG values were 0.55 mm (6X), 0.70 mm (6FFF), and −1.00 mm (10FFF). Validation confirmed good agreement between Mobius3D, Eclipse, and measurements. Clinical validation demonstrated high gamma pass rates and improved DVH metrics, particularly with the SRS 1 mm grid for small or heterogeneous targets. Conclusions: This workflow provides an example of Mobius3D software adaptation for routine IMRT/VMAT plan QA, enhancing accuracy and clinical reliability.