Application of TOPAS in dose calculations of low energy X-ray therapy machines

TOPAS (TOol for PArticle Simulation) is a Monte Carlo tool initially designed for simulating proton therapy machines. This study aims to investigate TOPAS’s applicability and accuracy in simulating orthovoltage therapy machine. An Xstrahl 300 orthovoltage machine was simulated. Spectra, HVLs (Half Value Layers), PDDs (Percentage Depth Doses), dose profiles, and backscatter factors were calculated for 100, 180, and 300 kVp. In addition, 3D (Three-Dimensional) dose distributions on a cranial CT (Computed Tomography) were assessed for a 5 cm diameter field size in different treatment locations. Where applicable, comparisons against other measurements or calculations are presented. ”TrackLengthEstimator” method was employed to investigate the dose distributions in regions of interest. Spectra, except for fluorescent peaks, agree with SpekPy (An X-ray spectrum calculator) calculations. HVLs, PDDs, and dose profiles show agreement with clinical measurements. Backscatter factors for four field sizes (1, 3, 5, and 10 cm diameter) and all energies show agreement (difference <2%) with published data. Visualization of dose distributions and DVHs (Dose Volume Histograms) on clinical CT sets are accessible functionalities. TOPAS is a robust Monte Carlo simulation tool for simulations of an orthovoltage treatment unit and could allow accessible visualization of 3D dose distributions in clinical plans. • Orthovoltage unit is characterized using TOPAS simulation tool. • TOPAS is employed to study the dose in a patient. • TOPAS results are verified by measurement or another Monte Carlo method. • This work explores TOPAS capability for in-house orthovoltage treatment planning.