Platform-Dependent Differences in Beam Characteristics and Low-Dose Exposure: A Comparative Study of Elekta™ Synergy...

Background/Objectives: Inter-platform variability in beam characteristics and low-dose exposure may arise from differences in linear accelerator head design, multileaf collimator geometry, and dose calculation algorithms. This study aimed to evaluate system-level dosimetric differences between two widely used linear accelerator platforms under clinically commissioned conditions. Methods: A comparative dosimetric analysis was performed between Elekta Synergy and Varian TrueBeam linear accelerators. Beam data were acquired using a SunSCAN™ 3D water phantom, and patient-specific quality assurance was conducted with the Octavius^® 4D system. Treatment plans were generated for left-sided breast, prostate, and head and neck cases using clinically commissioned treatment planning systems. Beam flatness, symmetry, penumbra width, low-dose exposure, conformity, homogeneity, and organ-at-risk dose metrics were evaluated. Results: Platform-dependent differences were observed in penumbra behavior and out-of-field dose, primarily attributable to intrinsic linac head design and collimation characteristics. These differences propagated into clinical plans, with greater variability observed for breast and head and neck cases, while prostate plans showed higher consistency between platforms. Algorithm-dependent trends were noted for conformity and homogeneity indices; however, all plans met institutional clinical acceptance criteria during quality assurance. Stricter gamma evaluation criteria revealed systematic but limited inter-platform deviations. Conclusions: Elekta Synergy and Varian TrueBeam demonstrated clinically acceptable dosimetric performance, with modest platform-dependent differences. While target coverage and overall plan quality were comparable, these variations were primarily observed in peripheral dose regions and may be relevant for platform-specific planning optimization and quality assurance. This supports the importance of comprehensive commissioning and QA procedures in both mixed- and single-platform clinical settings, particularly for highly modulated techniques.