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Interactions of Charged Particles with Matter
Published in W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald, Handbook of Radiotherapy Physics, 2021
Coulomb interactions with the bound atomic electrons are the principal way by which charged particles (electrons, protons, etc.) lose energy in the materials and energies of interest in radiotherapy. The particle creates a trail of ionisations and excitations along its path (see Section 1.4). Occasionally, the energy transfer to the atomic electron is sufficient to create a so-called delta ray (or δ-ray), which is a (secondary) electron with an appreciable range of its own. This is schematically illustrated in Figure 3.1. A fuller account of the theory of inelastic collisions between fast charged particles and atomic electrons can be found in Evans (1955) and in Andreo et al. (2017), Chapter 2.
X-rays, X-ray tube and X-ray Circuit
Published in Ken Holmes, Marcus Elkington, Phil Harris, Clark's Essential Physics in Imaging for Radiographers, 2021
In the case of ionisation, the released electron is known as a delta-ray and carries with it kinetic energy donated during the interaction. The delta-ray will go on to interact with other atoms until it has lost its acquired kinetic energy at which point it becomes indistinguishable from other electrons in the material.
Fundamental Concepts and Quantities
Published in Shaheen A. Dewji, Nolan E. Hertel, Advanced Radiation Protection Dosimetry, 2019
As discussed earlier, large fractions of energy can be transferred with scatter interactions. In the event that an incident electron approaches an atom within the radius of the electron cloud, the probability that it will interact directly with an orbital electron is significant. Since the orbital binding energy of the electron is typically very small compared with incident electron energies, the orbital electron can be treated as free. In this case, Equation (2.39) holds and the maximum energy transfer is high. The orbital electron may then be ionized, resulting in a delta ray, and this delta ray may then undergo additional interactions and create other ionizations along its path. Ionized inner-shell electrons will also result in subsequent decays of the electron shell, including the production of characteristic X-rays.
Biological effects of passive scattering and spot scanning proton beams at the distal end of the spread-out Bragg peak in single cells and multicell spheroids
Published in International Journal of Radiation Biology, 2021
Kento Nomura, Hiromitsu Iwata, Toshiyuki Toshito, Chihiro Omachi, Junpei Nagayoshi, Koichiro Nakajima, Hiroyuki Ogino, Yuta Shibamoto
The regions just before the dose falls off from the plateau of SOBP was defined as the distal end. The Geant4 (10.4-patch 2 version) Monte Carlo simulation was used to calculate LET, as described previously (Hashimoto et al. 2018). The physics model for the hadron and ion inelastic process is binary cascade, and the range cut is 1 km to cut off the delta-ray production in the simulation. The geometrical setup and beam settings were equivalent to those in the single cell and spheroid experiments (178.2–221.4 MeV for scanning and 250 MeV for passive scattering). For the dose-averaged LET calculation (Guan et al. 2015b), the information about track length and deposited energy in the target is scored in 1-mm grids. In the simulation, we used only protons for LET calculation according to Grassberger and Paganetti (2011) and their statistical error corresponding to Monte Carlo simulations was about 0.1–0.8% for spot scanning beams and 0.2–1.6% for passive scattering beams. The difference in the error between the two beams was probably due to the difference in the number of simulations. LET values from primary and subsequently produced (including secondary and tertiary) protons were calculated. Secondary electrons and other ion particles were disregarded. The LET profile of the two beam options was obtained at various water depths through SOBP to the distal end and fall-off region.
Targeting chemo-proton therapy on C6 cell line using superparamagnetic iron oxide nanoparticles conjugated with folate and paclitaxel
Published in International Journal of Radiation Biology, 2018
Seong Hee Kang, Seong Pyo Hong, Bo Sun Kang
As shown in Figure 8(a), cell apoptosis induced by TCPT using synthesized NPDDS is predominant over the groups of sequential treatment. Quantitative understanding of radiosensitizing effect of PTX is shown in Figure 8(b). The lower cell survival fraction in SG5 than SG7 was induced because of the presence of PTX in NPDDS when the same dose of proton beam was exposed. It is consistent with the results of cycle assay and morphological observation. The enhancement of radiosensitizing effect by SPIONs in TCPT is shown in Figure 8(c). Cell survival fraction of SG6 is lower than that of SG1 because of the enhanced radiosensitizing effect enhanced by the accumulation of SPIONs within the cytoplasm. The lower survival fraction in SG7 than in SG6 is induced by the FA receptor medicated endocytosis of NPDDS (FA-PTX-D-SPION). In general, higher Z atoms absorb more energy than soft tissues because they interact more with radiation. Thus the SPIONs in NPDDS increase the radiation absorption of the cancer cells by increasing SPION-proton interactions and consequently increasing the release of secondary radiations such as characteristic X-rays, Auger electrons, or delta-ray within the cancer cell (Berbeco et al. 2012; Zygmanski et al. 2013; Luchette et al. 2014). Since the energies of secondary radiations are in low energy region, their energy could be absorbed and localized within a cell. This phenomenon induced by SPIONs in NPDDS increases radiation absorption of the cancer cells and consequently reduces the curative dose in TCPT.
Track to the future: historical perspective on the importance of radiation track structure and DNA as a radiobiological target
Published in International Journal of Radiation Biology, 2018
The frequency and spectrum of clustered DNA damage is not only dependent on LET, but also on particle type. It is the 3D distribution of energy deposition that is important, while LET is a 1D quantity. It is well known that different charged particles of the same LET can differ in their biological effectiveness for given dose, typically decreasing with increasing atomic number. This is due to a reduction in local energy density along the track associated with the greater range of the delta-ray electrons produced. For example, the maximum range of delta-rays for a 1.8 MeV α-particle is the order of 0.1 μm (with ∼90% of energy deposited within ∼10 nm), the delta-rays from a 1 GeV amu−1 Fe ion of similar LET (150 keV μm−1) are capable of producing low-LET damage up to a several millimeters away in neighboring cells.