title: Monte Carlo modeling in CT-based geometries: dosimetry for biological modeling experiments with particle beam radiation.
abstract: The space radiation environment imposes increased dangers of exposure to ionizing radiation, particularly during a solar particle event (SPE). These events consist primarily of low energy protons that produce a highly inhomogeneous dose distribution. Due to this inherent dose heterogeneity, experiments designed to investigate the radiobiological effects of SPE radiation present difficulties in evaluating and interpreting dose to sensitive organs. To address this challenge, we used the Geant4 Monte Carlo simulation framework to develop dosimetry software that uses computed tomography (CT) images and provides radiation transport simulations incorporating all relevant physical interaction processes. We found that this simulation accurately predicts measured data in phantoms and can be applied to model dose in radiobiological experiments with animal models exposed to charged particle (electron and proton) beams. This study clearly demonstrates the value of Monte Carlo radiation transport methods for two critically interrelated uses: (i) determining the overall dose distribution and dose levels to specific organ systems for animal experiments with SPE-like radiation, and (ii) interpreting the effect of random and systematic variations in experimental variables (e.g. animal movement during long exposures) on the dose distributions and consequent biological effects from SPE-like radiation exposure. The software developed and validated in this study represents a critically important new tool that allows integration of computational and biological modeling for evaluating the biological outcomes of exposures to inhomogeneous SPE-like radiation dose distributions, and has potential applications for other environmental and therapeutic exposure simulations.
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, 3400 Civic Center Blvd, 8-136 SCTR Philadelphia, PA 19104, USA.
authors.forename: Eric S
authors.initials: ES
authors.lastname: Diffenderfer
authors.forename: Derek
authors.initials: D
authors.lastname: Dolney
authors.forename: Maximilian
authors.initials: M
authors.lastname: Schaettler
authors.forename: Jenine K
authors.initials: JK
authors.lastname: Sanzari
authors.forename: James
authors.initials: J
authors.lastname: McDonough
authors.forename: Keith A
authors.initials: KA
authors.lastname: Cengel
mesh_terms: D003198:Computer Simulation; D006801:Humans; D008954:Models, Biological; D015233:Models, Statistical; D009010:Monte Carlo Method; D010315:Particle Accelerators; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D011882:Radiotherapy, High-Energy / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: Monte Carlo; animal models; dosimetry; inhomogeneous dose distribution; radiobiology; solar particle event; stopping beams