Purpose: Monte Carlo simulations offer a powerful way to investigate and control processes in radiation processing, but need to accurately reflect the real-life situation to provide maximum value. Specifically, the time evolution of a process needs to be fully simulated, and this work reports on the incorporation of the time domain in EGSnrc radiation transport simulations. This advance allows for arbitrary, continuous motion of geometries, chronological simulation viewing, and synchronization of various simulation elements.

Methods: Arbitrary motion of geometries was added to the C++ class library in EGSnrc. Denoted EGS_DynamicGeometry, it allows the user to specify any existing geometry in the simulation upon which to apply time-dependent translations and rotations. Modifications to the EGSnrc code system facilitate the synchronization of dynamic objects in time and the recording of particle track time indices for chronological reconstruction. Furthermore, the 3D viewing tool egs_view was enhanced to visualize simulation time evolution, allowing the inspection of instantaneous tracks and configurations.

Results: Synchronized motion of geometries and sources was found to pass validity tests at the appropriate level. A range of realistic motion scenarios were investigated, involving multiple moving elements, with no identifiable systematic issues. Statistical uncertainty challenges associated with variable-speed motion were noted and further work is ongoing to optimize this uncertainty/motion problem.

Conclusions: Dynamic motion and chronological simulation analysis were successfully implemented, and provide valuable new functionality for modelling a wide range of experimental ionizing radiation scenarios in radiation processing.