title: Increasing the speed of DOSXYZnrc Monte Carlo simulations through the introduction of nonvoxelated geometries.
abstract: This article presents a method for increasing the speed of DOSXYZnrc Monte Carlo simulations through the introduction of nonvoxelated geometries defined in any coordinate system. Nonvoxelated geometries are used to isolate regions of uniform density and composition from the scoring grid. Particle transport within these geometric regions is not restricted by the boundary constraints of the scoring grid. This allows for larger particle steps, which in turn reduces the calculation time. A water tank phantom, water-lung interface phantom, cylindrical calibration phantom, and CT phantom were each used to test the application of the nonvoxelated approach. Each phantom was simulated using both the original DOSXYZnrc code and the new nonvoxelated code. The equivalence between the original and nonvoxelated simulations were quantified using a chi2 analysis. To within the statistical uncertainty, the voxelated and nonvoxelated simulations were found to give nearly identical results, regardless of boundary crossing algorithm. The speed increase was found to be a function of both voxel dimension and field size. Using nonvoxelated geometries and the EXACT boundary crossing algorithm, the speed increase was as high as 9.0, 5.1, 5.7, and 1.3 times faster for the water tank, water-lung interface, cylindrical calibration, and CT phantoms, respectively. If the PRESTA-I boundary crossing algorithm was used, the calculation speed increase was up to 6.0, 2.7, 3.3, and 1.2 times faster. These results clearly show that the nonvoxelated technique greatly increases simulation speed without any loss in dose accuracy.
authors.affiliation: Department of Physics, University of Saskatchewan, 116 Science Place, Saskatoon, Saskatchewan S7N 5E2, Canada. kkb628@mail.usask.ca
authors.forename: Kerry
authors.initials: K
authors.lastname: Babcock
authors.forename: Gavin
authors.initials: G
authors.lastname: Cranmer-Sargison
authors.forename: Narinder
authors.initials: N
authors.lastname: Sidhu
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D008954:Models, Biological; D015233:Models, Statistical; D009010:Monte Carlo Method; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*; D012680:Sensitivity and Specificity; D012984:Software; D013997:Time Factors