Validation of Radiobiological Monte Carlo Simulations Using the Dicentric Chromosome Assay Modified for Human Dermal Fibroblast Cells
Abstract
Purpose
Biodosimetry (BD) correlates biological damage from radiation exposure to absorbed dose, providing an accurate method of dose assessment that accounts for individual biological factors. The goal of this project is to modify an existing lymphocyte BD methodology for fibroblast cells to produce a dose response curve with X-rays. These curves can then be used to validate computational simulations that we previously developed.
Methods
Dermal fibroblasts were grown and irradiated to doses in the range of 0-4 Gy for X-ray energies 120 kV and 250 kV. Key experimental parameters in the Dicentric Chromosome Assay (DCA) were optimized. Additionally, the Cytokinesis-Block MicroNucleus assay was used to determine the percentage of cells in second mitosis. The radiation damage from X-rays at a cellular level was simulated with TOPAS-nBio. This output was used in the Mechanistic DNA Repair and Survival (MEDRAS) model to simulate DNA repair and endpoints of interest.
Results
The DCA methodology was optimized by adding sodium citrate at a 1:1 ratio with KCl for the hypotonic solution, removing BrdU from the protocol, and using a colcemid concentration of 0.1 μg/mL for 3 hours. With these optimized conditions, metaphase spreads were created and damage (dicentric yield) scored to create a successful calibration curve with aberration yields ranging from 0.0033-0.17 dicentrics/cell (dependent on energy/dose). Simulations have been completed for 250 kV X-rays, the calculated yields for which range from 0.034-0.54 dicentrics/cell. Additionally, simulations using 120 kV are currently underway.
Conclusion
The experimental dose response is lower than simulation results and the literature. There are significant interlaboratory differences in the literature, so this discrepancy is expected, but also highlights the importance of generating a curve using our own techniques for code validation. Moving forward, these simulations will be extended to more complex radiation sources such as the space environment or accidents.