scholarly journals Electron and Photon Energy Spectra Outside of 6 MV X-ray Small Radiotherapy Field Edges Produced by a Varian iX Linac

2021 ◽  
Vol 9 ◽  
Author(s):  
Nahum Xicohténcatl-Hernández ◽  
Adriana Moreno-Ramirez ◽  
Guerda Massillon-JL
Keyword(s):  
Beam Quality ◽  
Absorbed Dose ◽  
High Energy ◽  
Primary Electron ◽  
Radiological Protection ◽  
X Ray ◽  
Low Energy Electrons ◽  
Treatment Volume ◽  
Field Edge ◽  
Modern Radiotherapy

Due to the increase in the survival probability for patients treated with modern radiotherapy techniques to live enough for experimenting the late radiation effect, low dose outside the treatment volume becomes a concern. However, besides the absorbed dose, the beam quality outside the field edge should be taken into account. This work aimed at investigating the photon and electron fluence spectra outside the field edges for several small radiotherapy fields for determining the quality of the beams in order to better evaluate the secondary effect after modern radiotherapy treatments. Phase-space files of a 6 MV X-ray beam produced by a Varian iX linac for eight small fields of 0.7 × 0.7 cm2, 0.9 × 0.9 cm2, 1.8 × 1.8 cm2, 2.2 × 2.2 cm2, 2.7 × 2.7 cm2, 3.1 × 3.1 cm2, 3.6 × 3.6 cm2, and 4.5 × 4.5 cm2 and for the reference 10 × 10 cm2 field at SSD = 100 cm were generated using the BEAMnrc code. The photon and electron fluences in each field were calculated at 0.15, 1.35, and 9.85 cm water depth and several off-axis distances using FLURZnrc. The number of low-energy electrons between 1 and 10 keV at 2 cm outside the field edge increases by 60% compared to the central axis. Due to the relatively high linear energy transfer (LET) of these electrons, the results of this work should help to better evaluate the possible late effect of secondary radiation on healthy organs close to the tumor volume after radiotherapy treatment. We also observed high-energy electrons outside the field edge that are attributed to the leakage of the primary electron beam from the head of the linac. From a standpoint of radiological protection, these electrons should be taken into account when evaluating the dose delivered to the patient’s skin.

Absorbed-dose beam quality conversion factors for cylindrical chambers in high energy photon beams

2000 ◽  
Vol 27 (12) ◽  
pp. 2763-2779 ◽  
Author(s):  
J. P. Seuntjens ◽  
C. K. Ross ◽  
K. R. Shortt ◽  
D. W. O. Rogers
Keyword(s):  
Beam Quality ◽  
Absorbed Dose ◽  
High Energy ◽  
High Energy Photon ◽  
Photon Beams ◽  
Energy Photon ◽  
Conversion Factors

scholarly journals Symmetric and triangle-shaped variability of blazars

2014 ◽  
Vol 10 (S313) ◽  
pp. 97-98
Author(s):  
Kenji Yoshida
Keyword(s):  
Gamma Ray ◽  
High Energy ◽  
Low Energy ◽  
Light Curves ◽  
X Ray ◽  
High Energy Electrons ◽  
Flux Variability ◽  
Low Energy Electrons ◽  
Flux Increase ◽  
Rise Phase

AbstractSymmetric and triangle-shaped flux variability in X-ray and gamma-ray light curves is observed from many blazars. We derived the X-ray spectrum changing in time by using a kinetic equation of high energy electrons. Giving linearly changing the injection of low energy electrons into accelerating and emitting region, we obtained the preliminary results that represent the characteristic X-ray variability of the linear flux increase with hardening in the rise phase and the linear decrease with softening in the decay phase.

NOVEL ‘PHOTONEUTRON VOLUME DOSE EQUIVALENT’ HYPOTHESIS AND METHODOLOGY FOR SECOND PRIMARY CANCER RISK ESTIMATION IN HIGH-ENERGY X-RAY MEDICAL ACCELERATORS

2020 ◽  
Vol 188 (4) ◽  
pp. 432-443 ◽  
Author(s):  
Mehdi Sohrabi ◽  
Amir Hakimi
Keyword(s):  
Risk Estimation ◽  
High Energy ◽  
Second Primary ◽  
Radiological Protection ◽  
Primary Cancer ◽  
Second Primary Cancer ◽  
Dose Equivalent ◽  
X Ray ◽  
Risk Estimates ◽  
First Time

Abstract A novel ‘photoneutron (PN) volume dose equivalent’ methodology was hypothesized and applied for the first time for estimating PN second primary cancer (PN-SPC) risks in high-energy X-ray medical accelerators. Novel position-sensitive mega-size polycarbonate dosimeters with 10B converter (with or without cadmium covers) were applied for determining fast, epithermal and thermal PN dose equivalents at positions on phantom surface and depths. The methodology was applied to sites of tumors such as brain, stomach and prostate in 47 patients. The PN-SPC risks were estimated for specific organs/tissues using linear International Commission on Radiological Protection cancer risks and were compared with some available data. The corresponding PN-SPC risk estimates ranged from 1.450 × 10−3 to 1.901 cases per 10 000 persons per Gray. The method was applied to 47 patients for estimating PN-SPC risks in patients undergoing radiotherapy. The PN-SPC risk estimates well match those calculated by simulation but are comparatively different from those estimated by ‘PN point dose equivalent’ methods, as expected.

scholarly journals Beamline P02.1 at PETRA III for high-resolution and high-energy powder diffraction

2015 ◽  
Vol 22 (3) ◽  
pp. 675-687 ◽  
Author(s):  
Ann-Christin Dippel ◽  
Hanns-Peter Liermann ◽  
Jan Torben Delitz ◽  
Peter Walter ◽  
Horst Schulte-Schrepping ◽  
...  
Keyword(s):  
High Resolution ◽  
Powder Diffraction ◽  
Early Stage ◽  
Beam Quality ◽  
High Energy ◽  
Real Space ◽  
Photon Flux ◽  
X Rays ◽  
Ambient Conditions ◽  
X Ray

Powder X-ray diffraction techniques largely benefit from the superior beam quality provided by high-brilliance synchrotron light sources in terms of photon flux and angular resolution. The High Resolution Powder Diffraction Beamline P02.1 at the storage ring PETRA III (DESY, Hamburg, Germany) combines these strengths with the power of high-energy X-rays for materials research. The beamline is operated at a fixed photon energy of 60 keV (0.207 Å wavelength). A high-resolution monochromator generates the highly collimated X-ray beam of narrow energy bandwidth. Classic crystal structure determination in reciprocal space at standard and non-ambient conditions are an essential part of the scientific scope as well as total scattering analysis using the real space information of the pair distribution function. Both methods are complemented byin situcapabilities with time-resolution in the sub-second regime owing to the high beam intensity and the advanced detector technology for high-energy X-rays. P02.1's efficiency in solving chemical and crystallographic problems is illustrated by presenting key experiments that were carried out within these fields during the early stage of beamline operation.

Estimating the absolute flux distribution for a synchrotron X-ray beam using ionization-chamber measurements with various filters

2017 ◽  
Vol 24 (5) ◽  
pp. 939-953 ◽  
Author(s):  
Andrew W. Stevenson ◽  
Francesca Di Lillo
Keyword(s):  
Ionization Chamber ◽  
Flux Distribution ◽  
Beam Quality ◽  
Absorbed Dose ◽  
Absorbed Dose Rate ◽  
X Ray ◽  
Absolute Flux ◽  
The Absolute ◽  
Using Data ◽  
Chamber Measurements

It is shown that an extensive set of accurate ionization-chamber measurements with a primary polychromatic synchrotron X-ray beam transmitted through various filter combinations/thicknesses can be used to quite effectively estimate the absolute flux distribution. The basic technique is simple but the `inversion' of the raw data to extract the flux distribution is a fundamentally ill-posed problem. It is demonstrated, using data collected at the Imaging and Medical Beamline (IMBL) of the Australian Synchrotron, that the absolute flux can be quickly and reliably estimated if a suitable choice of filters is made. Results are presented as a function of the magnetic field (from 1.40 to 4.00 T) of the superconducting multi-pole wiggler insertion device installed at IMBL. A non-linear least-squares refinement of the data is used to estimate the incident flux distribution and then comparison is made with calculations from the programsSPECTRA,XOPandspec.exe. The technique described is important not only in estimating flux itself but also for a variety of other, derived, X-ray properties such as beam quality, power density and absorbed-dose rate. The applicability of the technique with a monochromatic X-ray beam for which there is significant harmonic contamination is also demonstrated. Whilst absolute results can also be derived in this monochromatic beam case, relative (integrated) flux values are sufficient for our primary aim of establishing reliable determinations of the percentages of the various harmonic components.

Influence of Tilt Angle on Hole Count and Secondary Fluorescence in x-ray Microanalysis

1990 ◽  
Vol 48 (2) ◽  
pp. 462-463
Author(s):  
E. A. Kenik ◽  
J. Bentley
Keyword(s):  
Tilt Angle ◽  
High Energy ◽  
Primary Electron ◽  
Objective Lens ◽  
X Rays ◽  
Bremsstrahlung Radiation ◽  
X Ray ◽  
Backscattered Electrons ◽  
The Magnetic Field ◽  
Secondary Fluorescence

The spatial resolution and accuracy of X-ray microanalysis in an analytical electron microscope (AEM) are limited by a variety of factors, two of which are the hole count and secondary fluorescence. The hole count arises from uncollimated radiation, either electrons or X rays, which excites areas of the specimen other than that excited by the primary electron beam. This can result in X-ray generation even when the probe does not hit the specimen; hence the name hole count. Secondary fluorescence deals with X-ray generation resulting from radiation produced by the interaction of the incident probe with the specimen. This radiation may be either backscattered electrons spiraling in the magnetic field of the objective lens or high energy X rays, particularly forward-peaked bremsstrahlung radiation. As the interaction of both the uncollimated radiation and the secondary radiation with the specimen can be influenced by the tilt angle of the specimen, the variation of the hole count and secondary fluorescence with specimen tilt was investigated.

scholarly journals A feasibility study on the use of phantoms with statistical lung masses for determining the uncertainty in the dose absorbed by the lung from broad beams of incident photons and neutrons

2017 ◽  
Vol 58 (3) ◽  
pp. 313-328 ◽  
Author(s):  
Atiyeh Ebrahimi Khankook ◽  
Hashem Miri Hakimabad ◽  
Laleh Rafat Motavalli
Keyword(s):  
Neutron Beam ◽  
Computational Models ◽  
Anatomical Variation ◽  
Absorbed Dose ◽  
High Energy ◽  
Low Energy ◽  
Radiological Protection ◽  
Energy Photon ◽  
Organ Volume ◽  
Photon Sources

Abstract Computational models of the human body have gradually become crucial in the evaluation of doses absorbed by organs. However, individuals may differ considerably in terms of organ size and shape. In this study, the authors sought to determine the energy-dependent standard deviations due to lung size of the dose absorbed by the lung during external photon and neutron beam exposures. One hundred lungs with different masses were prepared and located in an adult male International Commission on Radiological Protection (ICRP) reference phantom. Calculations were performed using the Monte Carlo N-particle code version 5 (MCNP5). Variation in the lung mass caused great uncertainty: ~90% for low-energy broad parallel photon beams. However, for high-energy photons, the lung-absorbed dose dependency on the anatomical variation was reduced to <1%. In addition, the results obtained indicated that the discrepancy in the lung-absorbed dose varied from 0.6% to 8% for neutron beam exposure. Consequently, the relationship between absorbed dose and organ volume was found to be significant for low-energy photon sources, whereas for higher energy photon sources the organ-absorbed dose was independent of the organ volume. In the case of neutron beam exposure, the maximum discrepancy (of 8%) occurred in the energy range between 0.1 and 5 MeV.

scholarly journals Measurements of doses from photon beam irradiation and scattered neutrons in an anthropomorphic phantom model of prostate cancer: a comparison between 3DCRT, IMRT and tomotherapy

Nukleonika ◽  
2017 ◽  
Vol 62 (1) ◽  
pp. 29-35 ◽  
Author(s):  
Anna Kowalik ◽  
Weronika Jackowiak ◽  
Julian Malicki ◽  
Małgorzata Skórska ◽  
Marta Adamczyk ◽  
...  
Keyword(s):  
Therapeutic Dose ◽  
Organs At Risk ◽  
Rapid Development ◽  
Intensity Modulated Radiotherapy ◽  
High Energy ◽  
Photon Beam ◽  
Beam Irradiation ◽  
X Ray ◽  
Field Edge ◽  
Scattered Neutrons

Abstract Introduction. The rapid development of new radiotherapy technologies, such as intensity modulated radiotherapy (IMRT) or tomotherapy, has resulted in the capacity to deliver a more homogenous dose in the target. However, the higher doses associated with these techniques are a reason for concern because they may increase the dose outside the target. In the present study, we compared 3DCRT, IMRT and tomotherapy to assess the doses to organs at risk (OARs) resulting from photon beam irradiation and scattered neutrons. Material and methods. The doses to OARs outside the target were measured in an anthropomorphic Alderson phantom using thermoluminescence detectors (TLD 100) 6Li (7.5%) and 7Li (92.5%). The neutron fluence rate [cm−2·s−1] at chosen points inside the phantom was measured with gold foils (0.5 cm diameter, mean surface density of 0.108 g/cm3). Results. The doses [Gy] delivered to the OARs for 3DCRT, IMRT and tomotherapy respectively, were as follows: thyroid gland (0.62 ± 0.001 vs. 2.88 ± 0.004 vs. 0.58 ± 0.003); lung (0.99 ± 0.003 vs. 4.78 ± 0.006 vs. 0.67 ± 0.003); bladder (80.61 ± 0.054 vs. 53.75 ± 0.070 vs. 34.71 ± 0.059); and testes (4.38 ± 0.017 vs. 6.48 ± 0.013 vs. 4.39 ± 0.020). The neutron dose from 20 MV X-ray beam accounted for 0.5% of the therapeutic dose prescribed in the PTV. The further from the field edge the higher the contribution of this secondary radiation dose (from 8% to ~45%). Conclusion. For tomotherapy, all OARs outside the therapeutic field are well-spared. In contrast, IMRT achieved better sparing than 3DCRT only in the bladder. The photoneutron dose from the use of high-energy X-ray beam constituted a notable portion (0.5%) of the therapeutic dose prescribed to the PTV.

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