Phototherapy Using Nanomaterials
D. Sakthi Kumar, Aswathy Ravindran Girija in Bionanotechnology in Cancer, 2023
X-rays can be used as efficient energy sources for initiating effective PDT. For this, scintillation nanoparticles (ScNps) with attached photosensitizers are employed, which serves the purpose of self-lighting photodynamic therapy (SLPDT) [208]. These materials can convert X-rays to UV-visible light and this concept improved the efficiency of PDT without employing an external light source. X-rays will be irradiated to the tumor site where the nano sensitizer systems have been accumulated. Upon irradiation, the encapsulated nanoparticles will emit light and this can be collected to activate the nearby PS. The scintillation process involves the conversion of incoming radiation into a large number of electron-hole pair and transfer of this electron-hole pair energy to the luminescent ions. Upon interaction with high energy photons with the lattice of ScNPs, many electron-hole pairs will be created and thermalized in the conduction and valence band respectively. Photoelectric effect and Compton Effect account for this interaction. Afterwards, these electron-hole pairs will migrate through the materials and repeated trapping at defects of these materials cause energy losses mainly due to non-radiative recombination. This will be followed by the final stage, which is luminescence, and here the energy from the SCNPs will excite the nearby PS causing 1O2 generation [209, 210].
Scintillation Counting
Graham Lappin, Simon Temple in Radiotracers in Drug Development, 2006
Modern counters use an external standard to measure quench. This method is common practice today and so will be covered in some detail. Before discussing the way that external standards work, however, the Compton scattering effect has to be explained. Arthur H. Compton was awarded the Nobel Prize in 1927 for the discovery of the effect named after him. Compton scattering is the scattering of photons of electromagnetic radiation from (quasi-)free electrons in matter. Upon absorption of γ irradiation, the solvent in a scintillation cocktail ejects electrons. These Compton electrons are ejected with a range of energies from zero to Emax, showing a characteristic Compton spectrum. The Compton electrons react with the scintillation cocktail, causing light to be emitted in a fashion analogous to the β-spectrum. Compton electrons and the resulting photons are subject to the same quench effects as the radionuclide in the sample. Thus, by measuring the shift in the Compton spectra, the amount of quench can be calculated.
Particles and Radiation
Rob Appleby, Graeme Burt, James Clarke, Hywel Owen in The Science and Technology of Particle Accelerators, 2020
In our scattering derivation above, we calculated the rate of scattering for high-frequency radiation; this was the Thomson scattering cross section. This is an elastic process in which the incident and scattered wavelengths are the same. However, we also know that individual photons carry momentum, and therefore should transfer some of that if they interact with an electron; this is the process that we call Compton scattering. Clearly, there must be some way of reconciling these two phenomena; we realise that Thomson scattering applies as long as the energy of the photon is much less than the rest energy of an electron, in other words . At higher frequencies the momentum transfer starts to become important and we have Compton scattering. In ordinary Compton scattering, a high-energy photon (with energy ϵi) is incident upon a stationary electron; the photon is scattered by an angle βcausing a recoil of the electron. The scattered photon therefore has a lower energy ϵf and a longer wavelength λf, given by the standard Compton formula
Monte Carlo-based calculation of nano-scale dose enhancement factor and relative biological effectiveness in using different nanoparticles as a radiosensitizer
Published in International Journal of Radiation Biology, 2021
Mostafa Robatjazi, Hamid Reza Baghani, Atefeh Rostami, Ali Pashazadeh
Although employing NPs as a radiosensitizer in high-energy X-ray radiotherapy is a useful approach for more efficient tumor cell killing, NP-assisted low-energy X-ray radiotherapy can result in more remarkable dose enhancement during the treatment. In this way, the results of the MC-based study by Kakade and Sharma (2015) demonstrated that the obtained dose enhancement factor (DEF) at the keV photon energy region is about 188% higher than that attained at MeV one when AuNPs are used during the irradiation. This fact is mainly linked to the large cross-sections of photoelectric interactions at low energy X-ray region, while the Compton scattering is the prevailing interaction at the high energy one. Therefore, the employed NPs during the low energy X-ray radiotherapy can act as promising and reliable radiosensitizers for dose enhancement purposes.
Estimation of energy absorption buildup factors of some human tissues at energies relevant to brachytherapy and external beam radiotherapy
Published in International Journal of Radiation Biology, 2019
The Monte Carlo simulation method was used to compare the obtained EABF values using MCNP6.1 (Goorley et al. 2012). MCNP6.1™ is a general-purpose, three-dimensional geometry, Monte Carlo radiation-transport code designed to track many particle types (Goorley et al. 2012). Thus, it is a general-purpose code for use in neutron, photon, and electron, etc. transport through different medium and in this work, it uses ENDF/B-VI.8 atomic data as the cross-section library. For calculation of the mfp of soft tissue and water, the mass attenuation coefficients were obtained using WinXCOM (Gerward et al. 2001, 2004). The mass energy absorption coefficients were obtained using data available at NIST (Hubbel and Seltzer 2004). For comparison, the soft tissue and the water were selected and their EABFs at 0.662 MeV (Cs-137 source), 1.173 and 1.25 MeV (Co-60 source) were obtained up to 20 mfp through MCNP simulation code assuming an isotropic photon source. The estimated error through the MCNP simulation was less than 1%. During the MCNP simulation, total and unscattered photon fluxes were calculated. In order to calculate the total photon flux, F2 tally was used while for unscattered photon flux, FT, FU, C and E cards were used besides F2 tally. FT and FU can count the number of interaction of photons with matter. C and E cards refer to angle of direction of photons and energy, respectively. Detailed explanation with more physics background (photoelectric effect, bound-electron Compton scattering, coherent scattering, bremsstrahlung photons, K and L X-rays, and pair production) can be found elsewhere (Rafiei and Tavakoli-Anbaran 2018).
Development of tumor-specific liposomes containing quantum dots-photosensitizer conjugate used for radiotherapy
Published in Journal of Liposome Research, 2022
M. Karabuga, S. Erdogan, S. S. Timur, I. Vural, S. Çalamak, K. Ulubayram
While ionizing radiation at keV energy levels is mostly used in imaging, high energy radiation types such as X or gamma rays in the MeV range are mostly used in treatment. The dominant radiation-matter interaction at keV and MeV energy levels is the photoelectric effect and Compton effect, respectively (Khan and Gibbons 2014). As nanoparticles such as QDs increase the electron density, they will increase the Compton effect. Increasing the Compton effect also means increasing the effectiveness of radiotherapy (Maggiorella et al.2012, Khan and Gibbons 2014). It has been reported that this effect is around 5% when QDs are used alone (Ishikawa and Biju 2011).
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