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Deterministic Radiation Transport Methods
Published in Jerry J. Battista, Introduction to Megavoltage X-Ray Dose Computation Algorithms, 2019
Although introduced recently to the field of radiotherapy dose calculations, transport theory has been applied to many areas of physics and engineering, due to the fact that particle transport processes arise in a wide variety of physical phenomena. The roots of transport theory can be traced back more than a century, when first used by Boltzmann to formulate the kinetic theory of gases (Boltzmann 1872). Subsequently, the theory was applied to derive the radiative transfer equation commonly used in astrophysics (Chandrasekhar 1960), in order to study the spectrum of radiation emerging from astronomical objects. More importantly, transport theory has been utilized to study neutron diffusion in nuclear reactor design and shielding calculations (Duderstadt and Martin 1979; Lewis and Miller 1984), where significant insight and progress have led to the development of novel numerical techniques and tools for solving the linear Boltzmann transport equation (Martin and Duderstadt 1977; Martin et al. 1981; Wareing et al. 2001; Adams and Larsen 2002). Such techniques have been adapted and made available to dose calculation algorithms for radiotherapy treatment planning (Williams et al. 2003; Boman et al. 2005; Hensel et al. 2006; Gifford et al. 2006; Vassiliev et al. 2008, 2010; Das 2015; Bouchard and Bielajew 2015; St Aubin et al. 2015, 2016).
Optical-CT Imaging
Published in George C. Kagadis, Nancy L. Ford, Dimitrios N. Karnabatidis, George K. Loudos, Handbook of Small Animal Imaging, 2018
Xueli Chen, Dongmei Chen, Fenglin Liu, Wenxiang Cong, Ge Wang, Jimin Liang
Cells encoded with the luciferase enzymes can serve as bioluminescent probes, which allow bioluminescent light emission. Because of the turbid nature of biological tissues, bioluminescent light is absorbed and scattered by the tissues when the light propagates in them. In a statistical sense, the propagation of the bioluminescent light can be accurately simulated with the Monte Carlo (MC) method (Wang et al. 1995; Li et al. 2004; Ren et al. 2010, 2013; Shen and Wang 2010). However, the MC method is time consuming. Recently, the massive parallel approach using general purpose graphic processing units has been adopted to speed up the MC simulation. The radiative transfer equation (RTE) is an analytic model to well describe photon propagation in biological tissues (Arridge 1999; Kim 2004; Klose and Larsen 2006; Cong et al. 2007; Cong and Wang 2010). Because the scattering of the photon transmission in the biological tissues predominates over the absorption, the propagation of bioluminescent photons can be described thoroughly by a diffusion approximation model (Cong et al. 2004a). The diffusion approximation model has been successfully applied for diffuse optical tomography (DOT), BLT, and FMT. Because the internal bioluminescent light is continuously on during the measurement, BLT operates only in the CW mode. In this case, the photon propagation in biological tissues can be described accurately by the steady-state diffusion equation (DE) and the Robin boundary condition (Cong et al. 2004b):
Functional Near-Infrared Spectroscopy
Published in Yu Chen, Babak Kateb, Neurophotonics and Brain Mapping, 2017
Carlos G. Treviño-Palacios, Karla J. Sanchez-Perez, Javier Herrera-Vega, Felipe Orihuela-Espina, Luis Enrique Sucar, Oscar Javier Zapata-Nava, Francisco F. De-Miguel, Guillermo Hernández-Mendoza, Paola Ballesteros-Zebadua, Javier Franco-Perez, Miguel Ángel Celis-López
Systems working in this modality have traditionally used derivations of the diffusion equation or direct derivations of the Boltzmann radiative transfer equation model of how light travels through highly scattering tissue (Arridge et al. 1992; Klose and Larsen 2006). This model allow not only to calculate the optical properties of bulk tissue but also to reconstruct chromophore concentrations in a 3D space (Scholkmann et al. 2014). There is more detailed information on the instrumentation for optical studies of tissue in the FD by Chance et al. (1998) and Fantini and Franceschini (2002).
Validating a simulation model for laser-induced thermotherapy using MR thermometry
Published in International Journal of Hyperthermia, 2022
Frank Hübner, Sebastian Blauth, Christian Leithäuser, Roland Schreiner, Norbert Siedow, Thomas J. Vogl
In general, the irradiation of laser light is modeled by the radiative transfer equationμa and μs are the absorption and scattering coefficients, respectively. In particular, as that radiative transfer happens significantly faster than temperature transfer, we neglect the time-dependence and use this quasi-stationary model. The scattering phase function 17])
Summary of numerical analyses for therapeutic uses of laser-activated gold nanoparticles
Published in International Journal of Hyperthermia, 2018
However, this review was concerned with gold nanoparticles and their application in thermal therapy mainly from the physical perspective viewpoint. The detailed descriptions contained herein dealt with the theoretical light activation of gold nanoparticles, consequent heat that is produced by irradiation, and the estimation of damage to cancer cells. As was described, these three processes can be modelled separately, depending on whether the researchers’ interests are only on one therapeutic parameter, or on a complex study that will yield an assessment of the entire therapeutic efficacy. First, researchers must strive with the irradiation of a tumour. A low, yet a sufficient light dose should be applied on the tumour to accomplish its complete removal without harming the surrounding healthy tissue. To achieve this task, several parameters have to be adjusted, such as the laser wavelength and power, and the dimensions and concentrations of nanoparticles. In this review, we focussed on extensively adopted modelling methods based on the radiative transfer equation. The equation was solved using the Monte Carlo method that constitutes a gold standard, and provides excellent accuracy in simulations. Owing to advances in parallel computing techniques (e.g. CUDA), the simulation duration time has been drastically reduced. State-of-the-art MC algorithms even offer great capabilities to handle curved boundaries and arbitrary-shaped media. Thus, this approach is perfectly suitable for absorbed energy estimation in PTT, but it still requires further development, e.g. to obtain Raman scattering spectra or fluorescence phenomena, which could be useful for gold nanoparticles used as contrast agents in imaging-guided therapy.