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Basic Atomic and Nuclear Physics
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
Gudrun Alm Carlsson, Michael Ljungberg
Three different types of forces are described by the standard model: (a) the strong force that holds the quarks together within the nucleus; (b) the electromagnetic force that results in the interactions between electrically charged particles; and (c) the weak force that interacts between subatomic particles and that can give rise to a radioactive decay of atoms. In addition to these three, there is also the force of gravity that brings objects with different masses together.
Proton and Other Heavy Charged-Particle Beams
Published in W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald, Handbook of Radiotherapy Physics, 2021
Alejandro Mazal, Ludovic de Marzi
The depth-dose and beam profile characteristics of a clinical proton beam are a consequence of the interactions of protons with matter. The main therapeutic potential of these beams is related to the huge energy deposition at the end of their track and their small scattering angle. Protons are charged particles that are relatively ‘heavy' compared with electrons (the mass of the proton, M, is 1836 times the mass, me, of the electron). Depending on their energy (also expressed as velocity), they interact with the medium through various mechanisms: inelastic or elastic interactions with the nucleus, with the bound atomic electrons and, for certain processes, with the whole atom. In clinical applications, protons are considered as having an intermediate energy, greater than 10−4M c2 (94 keV) and less than M c2 (940 MeV). A detailed discussion can be found in Bichsel (1968), and details about the main mechanisms of interaction between protons and matter can be found in Chapter 3.
Physics of Radiation Biology
Published in Kedar N. Prasad, Handbook of RADIOBIOLOGY, 2020
Electrons are negatively charged particles and orbit the atomic nucleus in a precisely defined path, each path being characterized by its own unique energy level. Electrons are positioned in shells or energy levels that surround the nucleus. The first or K shell contains no more than 2 electrons, the second or L shell no more than 8 electrons, and the third or M shell no more than 18 electrons (Figure 3.2). The outermost electron shell of an atom, no matter which shell it is, never contains more than 8 electrons. Electrons in the outermost shell are termed valence electrons and determine to a large degree the chemical properties of an atom. An atom with an outer shell filled with electrons seldom reacts chemically. These atoms constitute elements known as the inert gases (helium, neon, argon, krypton, xenon, and radon).
Dosimetric comparison between proton beam therapy, intensity modulated radiation therapy, and 3D conformal therapy for soft tissue extremity sarcoma
Published in Acta Oncologica, 2023
Brady S. Laughlin, Michael Golafshar, Matthew Prince, Wei Liu, Christopher J. Kutyreff, Safia K. Ahmed, Tamara Z. Vern Gross, Michael Haddock, Ivy Petersen, Todd A. DeWees, Jonathan B. Ashman
Proton beam therapy (PBT) may also be advantageous for eSTS patients with anatomically challenging presentations such as proximal medial thigh location or semi-circumferential tumor. Protons are heavy charged particles that undergo small angle scattering and deposit maximum energy per length close to the end of the range, termed the ‘Bragg’ peak [9]. PBT may be advantageous given the improved target conformality and reduction in integral dose [10–12]. In particular, PBT may lead to a reduction in dose to soft tissue and bone, allowing for a decreased risk of chronic lymphedema or late bone fracture. In this study, we performed a dosimetric comparison of pencil beam scanning PBT, IMRT, and 3D-CRT for patients with eSTS. We hypothesize that PBT will lead to better sparing of soft tissue and bone compared to IMRT and 3D-CRT.
Implementation of simplified stochastic microdosimetric kinetic models into PHITS for application to radiation treatment planning
Published in International Journal of Radiation Biology, 2021
Tatsuhiko Sato, Shintaro Hashimoto, Taku Inaniwa, Kenta Takada, Hiroaki Kumada
In treatment planning for BNCT, the absorbed doses deposited by 10B(n,α)7Li, 14N(n,p)14C, 1H(n,n)p, and photons are calculated separately (Kumada et al. 2004; Hopewell et al. 2011), which are referred to as boron, nitrogen, hydrogen, and photon components, respectively. The types and energies of the charged particles that contribute to each dose component are almost independent of the neutron spectra. Thus, 2018). Using the precalculated data, DB, DN, DH, and Dγ, respectively) are calculated from the particle transport simulation in the patient, using the track-length tally named [t-track] with the multiplier function. Note that the kerma approximation is used in the simulation (i.e. charged particles such as protons, He and Li ions as well as electrons are not transported).
Low dose ionizing radiation and the immune response: what is the role of non-targeted effects?
Published in International Journal of Radiation Biology, 2021
Annum Dawood, Carmel Mothersill, Colin Seymour
A damaging consequence of ionizing radiation is oxidative stress which can occur directly due to breaks in DNA structure by charged particles or indirectly via reactive chemical species generated due to bond breakage in non-DNA macromolecules (McMahon 2018) or via by-products from a water radiolysis reaction also generating free radicals and ROS (Azzam et al. 2012). This damage may migrate from the original site of radiation to nearby bystander cells through ‘redox-modulated intercellular communication mechanisms.’ (Azzam et al. 2012). LDIR induced oxidative stress may generate short and long-term ROS/RNS which can damage mitochondrial DNA (mtDNA) where genome alterations may be translated to various electron-transport chain subunits and relevant proteins (Rusin et al. 2018). When perturbations in oxidative metabolism reach abnormal levels, chronic inflammatory processes may initiate the recruitment of macrophages and neutrophils to the inflammation site where these immune cells release more ROS (Azzam et al. 2012). An increase in size and number of mitochondria per cell was also associated with radiation induced stress response leading to mitochondrial dysfunction upon direct irradiation (5 Gy) or through bystander factors that linger in the irradiated cell conditioned medium (ICCM) (Nugent et al. 2007) which may cause genomic instability in the future progeny (Kim et al. 2006).