A Monte Carlo Study on Dose Enhancement in the Presence of Nanoparticles by Photon Source: A Comparison between Various Concentration and Material of Nanoparticles

Purpose: Recently, the application of high atomic number nanoparticles is suggested in the field of radiotherapy to improve physical dose enhancement and hence treatment efficiency. Several factors such as concentration and material of nanoparticles and energy of beam define the amount of dose enhancement in the target in the presence of nanoparticles. Materials and Methods: In this approach, a spherical cell was simulated through the Geant4 Monte Carlo toolkit which contained a nucleus and nanoparticles distributed through the cell. To investigate the effect of the concentration of nanoparticles on the deposited dose, it ranged from 3 mg/g to 30 mg/g for different materials like gold, silver, gadolinium, and platinum. Also, various mono-energetic photon beams included low and high energy sources were applied. Results: The results proved that as the concentration increased, the Dose Enhancement Factor (DEF) enlarged. Overall, almost for all energy and material that were used in this study, the maximum of DEF values occurred in the concentration of 30 mg/g. Moreover, lower energy sources presented higher DEF compared to other sources. The results indicated that the highest amount of DEF transpired for 35 keV photon beams equal to 14.67. Also, the K-edge energy of each material affects DEF values. Conclusion: To obtain a better outcome in the use of nanoparticles in combination with radiotherapy, a higher concentration of nanoparticles and low-energy photons should be considered to optimize the DEF and thus the treatment ratio.

B d,s → $$ \gamma \mathrm{\ell}\overline{\mathrm{\ell}} $$ decay with an energetic photon

We calculate the differential branching fraction, lepton forward-backward asymmetry and direct CP asymmetry for Bd,s → $$ \gamma \mathrm{\ell}\overline{\mathrm{\ell}} $$ γ ℓ ℓ ¯ decays with an energetic photon. We employ factorization methods, which result in rigorous next-to-leading order predic- tions in the strong coupling at leading power in the large-energy/heavy-quark expansion, together with estimates of power corrections and a resonance parameterization of sub- leading power form factors in the region of small lepton invariant mass q2. The Bd,s → $$ \gamma \mathrm{\ell}\overline{\mathrm{\ell}} $$ γ ℓ ℓ ¯ decay shares features of the charged-current decay Bu → $$ \gamma \mathrm{\ell}{\overline{\nu}}_{\mathrm{\ell}} $$ γ ℓ ν ¯ ℓ ., and the FCNC decays B → $$ {K}^{\left(\ast \right)}\mathrm{\ell}\overline{\mathrm{\ell}} $$ K ∗ ℓ ℓ ¯ . As in the former, the leading-power decay rates can be expressed in terms of the B-meson light-cone distribution amplitude and short-distance factors. However, similar to B →$$ {K}^{\left(\ast \right)}\mathrm{\ell}\overline{\mathrm{\ell}} $$ K ∗ ℓ ℓ ¯ , four-quark and dipole operators contribute to the Bd,s → $$ \gamma \mathrm{\ell}\overline{\mathrm{\ell}} $$ γ ℓ ℓ ¯ decay in an essential way, limiting the calculation to q2 ≲ 6 GeV2 below the charmonium resonances in the lepton invariant mass spectrum. A detailed analysis of the main observables and theoretical uncertainties is presented.