Monte Carlo studies on neutron interactions in radiobiological experiments

Beni, Mehrdad Shahmohammadi; Hau, Tak Cheong; Krstić, Dragana; Nikezić, D.; Yu, K.N.

doi:10.1371/journal.pone.0181281

Cited by 12 publications

(8 citation statements)

References 18 publications

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“…The penetration fractions were reduced for larger medium thicknesses, which was explained by the presence of more atoms in the medium leading to larger probabilities of photon interactions. Similar trends were also observed in our previous works [ 15 , 16 ]. On the other hand, the penetration fractions were enhanced for larger incident photon energies, which was due to the reduced interaction cross-sections.…”

Section: Computation Scheme and Outputssupporting

confidence: 92%

“…The total energy-dependent photo-atomic cross-section data and energy-dependent cross-sections for each interaction mechanism shown in Fig 2 were obtained from the National Institute of Standards and Technology (NIST) XCOM library homepage: https://physics.nist.gov/PhysRefData/Xcom/html/xcom1.html . Similar to our previous works [ 15 , 16 ], photons with energies between 1 keV and 10 MeV were considered. The total photon cross-sections for 1 H, 12 C, 14 N and 16 O nuclei were obtained from the XCOM library homepage.…”

Section: Monte Carlo Methods and Nruphoton Codementioning

confidence: 99%

“…Event-by-event three-dimensional tracking of propagation of particles in water and cell domains were described in detail in our previous works [ 15 , 16 ], and would not be repeated here.…”

Section: Monte Carlo Methods and Nruphoton Codementioning

confidence: 99%

“…The areas under the curves for the angular distributions in Fig 13 , i.e., ( ), represented the integrated numbers of photons (referred to as “interacting photons”) that had exited the medium layer and subsequently underwent interactions within the cell layer [ 15 ]. From Fig 13 , it was noted that the areas under the curves increased with the water medium thickness.…”

Section: Computation Scheme and Outputsmentioning

confidence: 99%

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Monte Carlo studies on photon interactions in radiobiological experiments

et al. 2018

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X-ray and γ-ray photons have been widely used for studying radiobiological effects of ionizing radiations. Photons are indirectly ionizing radiations so they need to set in motion electrons (which are a directly ionizing radiation) to perform the ionizations. When the photon dose decreases to below a certain limit, the number of electrons set in motion will become so small that not all cells in an “exposed” cell population can get at least one electron hit. When some cells in a cell population are not hit by a directly ionizing radiation (in other words not irradiated), there will be rescue effect between the irradiated cells and non-irradiated cells, and the resultant radiobiological effect observed for the “exposed” cell population will be different. In the present paper, the mechanisms underlying photon interactions in radiobiological experiments were studied using our developed NRUphoton computer code, which was benchmarked against the MCNP5 code by comparing the photon dose delivered to the cell layer underneath the water medium. The following conclusions were reached: (1) The interaction fractions decreased in the following order: 16O > 12C > 14N > 1H. Bulges in the interaction fractions (versus water medium thickness) were observed, which reflected changes in the energies of the propagating photons due to traversals of different amount of water medium as well as changes in the energy-dependent photon interaction cross-sections. (2) Photoelectric interaction and incoherent scattering dominated for lower-energy (10 keV) and high-energy (100 keV and 1 MeV) incident photons. (3) The fractions of electron ejection from different nuclei were mainly governed by the photoelectric effect cross-sections, and the fractions from the 1s subshell were the largest. (4) The penetration fractions in general decreased with increasing medium thickness, and increased with increasing incident photon energy, the latter being explained by the corresponding reduction in interaction cross-sections. (5) The areas under the angular distribution curves of photons exiting the medium layer and subsequently undergoing interactions within the cell layer became smaller for larger incident photon energies. (6) The number of cells suffering at least one electron hit increased with the administered dose. For larger incident photon energies, the numbers of cells suffering at least one electron hit became smaller, which was attributed to the reduction in the photon interaction cross-section. These results highlighted the importance of the administered dose in radiobiological experiments. In particular, the threshold administered doses at which all cells in the exposed cell array suffered at least one electron hit might provide hints on explaining the intriguing observation that radiation-induced cancers can be statistically detected only above the threshold value of ~100 mSv, and thus on reconciling controversies over the linear no-threshold model.

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Section: Computation Scheme and Outputssupporting

confidence: 92%

Section: Monte Carlo Methods and Nruphoton Codementioning

confidence: 99%

“…Event-by-event three-dimensional tracking of propagation of particles in water and cell domains were described in detail in our previous works [ 15 , 16 ], and would not be repeated here.…”

Section: Monte Carlo Methods and Nruphoton Codementioning

confidence: 99%

Section: Computation Scheme and Outputsmentioning

confidence: 99%

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Monte Carlo studies on photon interactions in radiobiological experiments

et al. 2018

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“…The uncertainties shown as shades around the theoretical prediction curves were introduced by the Monte Carlo model. These uncertainties represented one standard deviations obtained from the multiplication of the relative error estimated using the (F6:P) tally by the tally mean value [15]. The slope of the calibration curve in Figure 8 was larger at smaller doses and tended to saturate at larger doses.…”

Section: Resultsmentioning

confidence: 99%

Modeling kV X-ray-Induced Coloration in Radiochromic Films

et al. 2018

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Commercially available radiochromic films are primarily designed for clinical X-ray dosimetry. These films change color upon exposures to radiation as a result of solid-state polymerization (SSP). Built on a previous model developed for SSP upon exposures to ultraviolet (UV) radiation, a new model was developed in the present work for X-ray-induced coloration in Gafchromic EBT3 films. Monte Carlo simulations using the Monte Carlo N-Particle (MCNP) code were employed to model the transport and interaction of photons and the generated secondary electrons within the film active layer. The films were exposed to continuous-energy photon beams. The dose D E in the external radiation detector (i.e., ionization chamber) was determined and the realistic dose D A in the film active layer was then obtained using the calibration coefficient R (=D A /D E ). The finite element method (FEM) was used to solve the classical steady-state Helmholtz equation using the multifrontal massively parallel sparse direct solver (MUMPS). An extensive grid independence test was carried out and the numerical stability of the present model was ensured. The reflected light intensity from the film surface was used to theoretically obtain the net reflective optical density of the film exposed to X-ray. Good agreement was obtained between the experimental and theoretical results of the net reflective optical density of the film. For X-ray doses >~600 cGy, due to the already formed densely cross-linked structure in the active layer of the EBT3 film so further bond formation was less likely, the reflected light intensity from the film surface increased at a relatively lower rate when compared to those for dose values <~600 cGy.

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