Formation of Dissipative Structures in an Amorphous Film

Malkov, V. B.; Nikolaenko, I. V.; Швейкин, Г. П.; Pushin, V. G.; Malkov, A. V.; Malkov, O. V.; Шульгин, Б. В.

doi:10.1134/s0012501618020033

Cited by 5 publications

(3 citation statements)

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“…Parallel-plate chambers have been widely used in measuring dose at the surface or build-up region in conventional linacs. With the magnetic field's presence, several parallel-plate chambers' dose response was examined by the Monte Carlo method, and magnetic field correction factors were calculated (Malkov andRogers 2018, Pojtinger et al 2018). Due to the parallel-plate chamber's radial symmetry design, there may be no angular dependence if the chamber rotates in the coronal plane while keeping the entrance window orthogonal to the beam.…”

Section: Introductionmentioning

confidence: 99%

“…Due to the parallel-plate chamber's radial symmetry design, there may be no angular dependence if the chamber rotates in the coronal plane while keeping the entrance window orthogonal to the beam. However, a 3°till of a Markus chamber resulted in a dose variation of 0.28% in the MR-Linac (Malkov and Rogers 2018). We further investigated the Advanced Markus' response in the magnetic field as a function of the angle between the entrance window and the beam.…”

Section: Introductionmentioning

confidence: 99%

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Effects on skin dose from unwanted air gaps under bolus in an MR-guided linear accelerator (MR-linac) system

et al. 2021

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Bolus is commonly used in MV photon radiotherapy to increase superficial dose and improve dose uniformity for treating shallow lesions. However, irregular patient body contours can cause unwanted air gaps between a bolus and patient skin. The resulting dosimetric errors could be exacerbated in MR-Linac treatments, as secondary electrons generated by photons are affected by the magnetic field. This study aimed to quantify the dosimetric effect of unwanted gaps between bolus and skin surface in an MR-Linac. A parallel-plate ionization chamber and EBT3 films were utilized to evaluate the surface dose under bolus with various gantry angles, field sizes, and different air gaps. The results of surface dose measurements were then compared to Monaco 5.40 Treatment Planning System (TPS) calculations. The suitability of using a parallel-plate chamber in MR-Linac measurement was validated by benchmarking the percentage depth dose and output factors with the microDiamond detector and air-filled ionization chamber measurements in water. A non-symmetric response of the parallel-plate chamber to oblique beams in the magnetic field was characterized. Unwanted air gaps significantly reduced the skin dose. For a frontal beam, skin dose was halved when there was a 5 mm gap, a much larger difference than in a conventional linac. Skin dose manifested a non-symmetric pattern in terms of gantry angle and gap size. The TPS overestimated skin dose in general, but shared the same trend with measurement when there was no air gap, or the gap size was larger than 5 mm. However, the calculated and measured results had a large discrepancy when the bolus-skin gap was below 5 mm. When treating superficial lesions, unwanted air gaps under the bolus will compromise the dosimetric goals. Our results highlight the importance of avoiding air gaps between bolus and skin when treating superficial lesions using an MR-Linac system.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects on skin dose from unwanted air gaps under bolus in an MR-guided linear accelerator (MR-linac) system

et al. 2021

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“…It is known that the formation of interblock boundaries take place with varying module of the misorientation vector  in NRSDS of hexagonal seleniumnanofine crystals after the stage of quenching of NRSDS's [1][2][3][4]. This phenomenon is the result of relaxation of an inhomogeneous elastic rotational curvature of the lattice around [001] in one of NRSDS block [5][6][7][8][9].…”

Section: Introductionmentioning

confidence: 99%

Phenomenon of relaxation of inhomogeneous elastic rotational curvature of the lattice of nanofine spatial dissipative structures of hexagonal selenium

Malkov

Chemezov

Pushin

et al. 2020

IOP Conf. Ser.: Mater. Sci. Eng.

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Nanofine rhomboid spatial dissipative structures (NRSDS) of hexagonal selenium were found and studied by means of transmission electron microscopy in amorphous Se films coated with nanofine layers of amorphous carbon, at a temperature of their thermo gradient treatment of 423 K. As a result, pictures were received of fan-shaped linear bending extinction contours on the electron-microscopic images of NRSDS. It was shown that in the above NRSDS take place continuous linear increase in the bend radius of the lattice along [001], due to continuous linear relaxation of the inhomogeneous elastic torsion of the lattice around [001]. The continuous linear relaxation of the elastic rotational curvature of the lattice around [001] in NRSDS of hexagonal selenium with inhomogeneous elastic rotational curvature of the lattice covers the entire nanofine rhomboid spatial dissipative structures, and not its part, as is the case with the formation of interblock boundaries in the nanofine rhomboid spatial dissipative structures.

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