Simulation of physical processes with Monte Carlo methods in the keV and MeV energy range

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The technological developments of modern medicine foster the need for detailed understanding of the physical processes involved. Physical models are the basis of research in medical physics and enable the development of fundamental methodology for the optimal use of novel technologies in radiotherapy and radiology. In radiotherapy, radiation beams are used to ionize the cellular environment and cause biological damage to eradicate tumors. Particles of interest composing therapeutic beams produce localized cascades of secondary particles, and their detailed transport in heterogeneous media needs to be simulated with Monte Carlo methods to predict the energy deposition in patients and standard environments to support personalized radiotherapy. In X-ray computed tomography (CT), patient geometries are investigated for the diagnosis of anomalies and for therapeutic interventions. Emerging applications of spectral CT involve the resolution of photon energy at the detector level which opens the way to a variety of advanced quantitative medical applications. To support this development, Monte Carlo methods are used extensively for their ability to simulate photon transport in the keV energy range, including the production of scatter and the simulation of radiation detector response converting X-rays into electric signal. Another challenging application in which Monte Carlo simulation is essential is MRI-guided radiotherapy. The promising integration of magnetic resonance imaging (MRI) to radiotherapy linacs adapt dose delivery to the target motion and other potential anatomical changes in real time. But MRI involves an external magnetic field that is strong enough to distort localized particle cascades produced by radiotherapy beams. Both radiation dose distributions and radiation detector response require the use of Monte Carlo methods to achieve accurate radiation dosimetry of MRI-guided radiotherapy beams. The main purpose of this research program is to explore various applications of Monte Carlo particle transport simulation that are relevant to modern medicine, in particular to radiotherapy and imaging. Technologies in radiotherapy and medical imaging are continuously evolving from which arises new challenges requiring careful understanding of the governing physical processes. The proposed research program will explore both practical and fundamental research in radiotherapy and medical imaging with Monte Carlo particle transport simulation. The impact of this research will contribute towards improved understanding of small and dynamic photon beams dosimetry, non-equilibrium MRI-guided radiation dosimetry, and emerging applications of spectral computed tomography.