Treatment planning
A mix of VMAT treatment sites consisting of a total of 118 clinical plans were randomly selected for this study. All treatment plans were created in RayStation version 10.A (RaySearch Medical Laboratories AB, Stockholm, Sweden) TPS with a grid size of 1 mm for intensity‐modulated radiosurgery (IMRS) cases and 2 mm for other treatment sites. The dose‐calculation algorithm was collapsed‐cone convolution version 5.3, and gantry angle sampling of 2° between the control points was used for all the optimized plans. Two Varian linacs (Edge and TrueBeam‐Varian Medical Systems, Palo Alto, CA) with 6 MV‐FFF, 6 MV, and 10 MV beams were utilized. Edge linac is equipped with high definition multileaf collimator (HD‐120 MLC), and TrueBeam has standard Millennium 120 MLC. A summary of the treatment plans showing beam energy, the number of beams, and the linac used for treatment are shown in Table The number of plans for each machine and energyAbbreviations: FFF, flattening filter free; H&N, head and neck; IMRS, intensity‐modulated radiosurgery; Med, mediastinum; SBRT, stereotactic body radiation therapy; SIMT, single isocenter multiple target; VMAT, volumetric‐modulated arc therapy.