Monte Carlo simulations of synchrotron X-ray dose effects on root growth during in-vivo tomographic imaging

Synchrotron X-ray computed tomography (XCT) has been increasingly applied to study the in-vivo dynamics of root growth and rhizosphere processes. However, minimizing radiation-induced damage to root growth warrants further investigation. Our objective was to develop a robust approach for modeling and evaluating ways to reduce synchrotron X-ray dose effects on root growth during in-vivo imaging. Wheat roots growing in soil were exposed to X-rays during XCT experiments resolved in space (3-D) plus time (4-D). The dose rate and cumulative absorbed dose in roots were modelled with the Monte Carlo code FLUKA considering different experimental conditions using polychromatic and quasi-monochromatic X-ray beam configurations. The most impactful factors affecting damage to roots were incident X-ray energy spectrum, stored current in the accelerator machine, position of the root in the soil, and possibly the number of exposures during the 4-D XCT experiments. Our results imply that radiation dose during in-vivo imaging of plant roots can be diminished by using monochromatic radiation at the highest energy suitable for a given sample thickness and field of view, and by controlling the rotation axis of off-centered roots to increase radiation protection by soil.