Beam data and model validation for Elekta SRS cone collimator in 6MV and 6MVFFF beams

This study aimed to evaluate the beam data of Elekta stereotactic radiosurgery (SRS) cone collimators for 6MV and 6MV flattening filter-free (6MVFFF) beams and to assess the feasibility of implementing a shared beam model across beam-matched linear accelerators (linacs). Percentage depth dose (PDD), beam profiles, and output factors were measured using IBA SFD and PTW microDiamond detectors for fixed (current clinical practice) and variable (previous clinical practice) jaw configurations. A Monaco X-ray voxelized Monte Carlo (XVMC)-based SRS model was developed on one linac and validated using SNC SRS MapCHECK and StereoPHAN^TM. The model's applicability was further tested on a second linac. The depth of maximum dose (D_max) and PDD beyond D_max decreased with smaller cones, while penumbra widened for larger cones. Compared to 6MVFFF, 6MV beams exhibited 5% higher in-field off-axis ratios (OARs) and 15% higher out-of-field OARs. The output factors for 6MVFFF exceeded those of 6MV by up to 5.83% (7.5-mm cone). Fixed jaw configurations increased out-of-field OARs by 15% and output factors by 0.57% compared to variable jaws. Measurements from IBA SFD and microDiamond detectors showed excellent agreement in PDD and beam profiles, with output factors differing by less than 2.33%. The Monaco XVMC model achieved >99.10% gamma passing rates (2%/2 mm) and <3.0% central axis point dose differences during validation. Both linacs demonstrated minimal discrepancies when using shared beam models. Fixed jaw settings increase out-of-field scatter and output factors for cones <35 mm. The comprehensive beam data for 6MV and 6MVFFF beams presented in this study provide a valuable reference for commissioning and quality assurance (QA) in clinical practice. IBA SFD and microDiamond detectors are suitable for SRS cone beam data collection and QA when appropriate corrections as per TRS-483 are applied. Shared beam models are feasible for beam-matched linacs, offering a streamlined approach to clinical work.