In radiation therapy with orthovoltage units, the tube design has a crucial effect on its dosimetric features. In this study, the effect of anode angle on photon beam spectra, depth dose and photon fluence per initial electron was studied for a commercial orthovoltage unit of X-RAD biological irradiator.
The photon beam spectra were calculated for anode angles from 15 to 35 degrees. We also calculated the percentage depth doses for some angles to verify the impact of anode angle on depth dose.
Additionally, the heel effect and its relation with anode angle were studied for X-RAD irradiator. Our results showed that the photon beam spectra and their mean energy are changed significantly with anode angle and the optimum anode angle of 30 degrees was selected based on less heel effect and appropriate depth dose and photon fluence per initial electron.
It can be concluded that the anode angle of 30 degrees for X-RAD unit used by manufacturer has been selected properly considering the heel effect and dosimetric properties. In spite of a considerable reduction in the application of orthovoltage X-ray units following the advent of electron linear accelerators in radiation therapy, they have found several applications in recent radiation therapy as well as radiobiological experiments.
The anode type and angle as well as filters play an influential role in photon beam spectra and, consequently, depth dose characteristics for orthovoltage radiotherapy units. The X-ray tube manufacturers design and optimize the tube structural plan based on multiple mechanical and radiation considerations. The anode angle has a determinant effect on photon beam intensity characteristics across the X-ray beam which is known as heel effect in X-ray tubes. On the other hand, changing the anode angle alters the X-ray absorption inside the tungsten target and photon beam spectra received by therapeutic beam are changed accordingly.
Monte Carlo MC modeling of X-ray units including kilovoltage and orthovoltage units has been done in several comprehensive studies. For instance, precise information regarding the absorbed dose distributions in water has a critical impact on the accuracy of results provided by means of dosimetry protocols. However, some MC studies have been performed to give rise to more detailed information about the effect of tube components on dosimetric characteristics including depth dose and photon beam spectra for a better and more efficient tube designation.
In an MC study by Verhaegen et al. Recent interest in radiation therapy with orthovoltage beams for animal studies, as well as the application of high atomic number contrast media, such as iodine in radiation therapy have been new motivations for MC modeling of these units.
In the current study, an MC model of X-RAD biological irradiator, which is being used currently for animal and cell culture irradiation, was built based on the manufacturer provided data.
The effect of anode angle on dosimetric properties of this unit was studied and the optimum anode angle was selected for the unit. Additionally, the validated MC model can be used either for further studies on its dosimetry or for the application of this unit for animal radiation therapy. This unit generates orthovoltage X-ray beams and routinely is used for irradiation of small animals and cell cultures in radiobiological studies.
The lead shielding of the tube was not simulated and the X-ray leakage effect was not considered in our simulations. The electron beam diameter was 2.
An anode angle of 30 was considered according to manufacturer's drawings. This setup remained constant in all simulations and in other simulations for an optimum anode angle determination; the only changing parameter was the anode angle. The schematic geometry of simulated tube and water phantom used for X-RAD biological irradiator. The statistical uncertainty of results was less than 1. The F6 tally scores the absorbed dose in terms of MeV per gram of tallying cells.
Absorbed dose inside the water phantom was scored for different anode angles. Because of modeling of low energy electrons and photons transport in this study, so as to avoid any bias in our results, no electron and photon energy cutoffs were used.
SpekCalc software version 1. This software has been developed using the results of comprehensive MC modeling of orthovoltage X-ray tubes used for radiation therapy. It is free and can be obtained by sending request to its producers. The interested reader can find more detailed information about this software in the article of Poludniowski et al. It can incorporate different types of filters and anode angles from 5 to 30 degrees in its calculations.
There was a close agreement between the results of both methods for the whole energy spectra. However, the small differences can be attributed to the different algorithms and cross-section files used for MCNPX code and SpekCalc software.
The results confirmed that our model is accurate and can be used for other MC applications, such as MC dose distribution calculations in water phantom. In Fig.X-ray spectroscopy is a general term for several spectroscopic techniques for characterization of materials by using x-ray excitation.
Factors affecting X-ray beam quality and quantity
When an electron from the inner shell of an atom is excited by the energy of a photon, it moves to a higher energy level. When it returns to the low energy level, the energy which it previously gained by the excitation is emitted as a photon which has a wavelength that is characteristic for the element there could be several characteristic wavelengths per element.
Analysis of the X-ray emission spectrum produces qualitative results about the elemental composition of the specimen. Comparison of the specimen's spectrum with the spectra of samples of known composition produces quantitative results after some mathematical corrections for absorption, fluorescence and atomic number.
Atoms can be excited by a high-energy beam of charged particles such as electrons in an electron microscope for exampleprotons see PIXE or a beam of X-rays see X-ray fluorescenceor XRF or also recently in transmission XRT. These methods enable elements from the entire periodic table to be analysed, with the exception of H, He and Li. In electron microscopy an electron beam excites X-rays; there are two main techniques for analysis of spectra of characteristic X-ray radiation: energy-dispersive X-ray spectroscopy EDS and wavelength dispersive X-ray spectroscopy WDS.
In an energy-dispersive X-ray spectrometer, a semiconductor detector measures energy of incoming photons. To maintain detector integrity and resolution it should be cooled with liquid nitrogen or by Peltier cooling. In a wavelength-dispersive X-ray spectrometer, a single crystal diffracts the photons according to Bragg's lawwhich are then collected by a detector.
By moving the diffraction crystal and detector relative to each other, a wide region of the spectrum can be observed. To observe a large spectral range, three of four different single crystals may be needed. While WDS is slower than EDS and more sensitive to the positioning of the sample in the spectrometer, it has superior spectral resolution and sensitivity.
WDS is widely used in microprobes where X-ray microanalysis is the main task and in XRF; it is widely used in the field of X-ray diffraction to calculate various data such as interplanar spacing and wavelength of the incident X-ray using Bragg's law.
The father-and-son scientific team of William Lawrence Bragg and William Henry Braggwho were Nobel Prize Winners, were the original pioneers in developing X-ray emission spectroscopy. Jointly they measured the X-ray wavelengths of many elements to high precision, using high-energy electrons as excitation source.
The cathode ray tube or an x-ray tube  was the method used to pass electrons through a crystal of numerous elements. They also painstakingly produced numerous diamond-ruled glass diffraction gratings for their spectrometers.
The law of diffraction of a crystal is called Bragg's law in their honor. Intense and wavelength-tunable X-rays are now typically generated with synchrotrons.
In a material, the X-rays may suffer an energy loss compared to the incoming beam. This energy loss of the re-emerging beam reflects an internal excitation of the atomic system, an X-ray analogue to the well-known Raman spectroscopy that is widely used in the optical region.
In the X-ray region there is sufficient energy to probe changes in the electronic state transitions between orbitals ; this is in contrast with the optical region, where the energy loss is often due to changes in the state of the rotational or vibrational degrees of freedom. For instance, in the ultra soft X-ray region below about 1 k eVcrystal field excitations give rise to the energy loss. The photon-in-photon-out process may be thought of as a scattering event. When the x-ray energy corresponds to the binding energy of a core-level electron, this scattering process is resonantly enhanced by many orders of magnitude.
Due to the wide separation of orbital energies of the core levels, it is possible to select a certain atom of interest. The small spatial extent of core level orbitals forces the RIXS process to reflect the electronic structure in close vicinity of the chosen atom.
Thus, RIXS experiments give valuable information about the local electronic structure of complex systems, and theoretical calculations are relatively simple to perform. There exist several efficient designs for analyzing an X-ray emission spectrum in the ultra soft X-ray region.
The figure of merit for such instruments is the spectral throughput, i. Usually, it is possible to change these parameters within a certain range while keeping their product constant. Henry Augustus Rowland — devised an instrument that allowed the use of a single optical element that combines diffraction and focusing: a spherical grating.
Reflectivity of X-rays is low, regardless of the used material and therefore, grazing incidence upon the grating is necessary.Purpose: This work investigated several topics related to dosimetry in soft tissue from fluoroscopic X-ray beams; first, it investigated the X-ray beam spectra and air kerma rates available for clinical use on state-of-the-art fluoroscopes using spectral copper [Cu] filtration; second, it investigated the fluoroscopic X-ray beam characteristics of first half-value layer HVLsecond HVL, homogeneity coefficients HCsand backscatter factors BSFs across the full range of available beam qualities; and third, it investigated the energy dependence of kerma-area-product KAP -meters measuring the radiation output of the fluoroscope.
Materials and Methods: A state-of-the-art Siemens Artis Zee fluoroscope was operated in the service mode to allow for manual control of the technique factors kVp, mA, ms, and Cu. BSFs were determined across a large range of X-ray field sizes and beam spectra with polymethyl-methacrylate. Percent depth doses PDDs and X-ray beam profiles were acquired across a similar range of X-ray beam spectra using a PTW water tank and a Spokas ionization chamber for the PDD measurements and a solid state dosimeter for the beam profile measurements.
Results: Fluoroscopic dose rate and technique parameter curves are reported for several state-of-the-art fluoroscopes, illustrating differences in approach among vendors and establishing the basis for investigation of the X-ray beam characteristics HVLs, HCs, BSFs, and PDDs. These X-ray beam characteristics are reported across a large range of clinically available X-ray beam spectra, providing the necessary foundation for dosimetry in soft tissue from these beams.
Additionally, the accuracy of the displayed Ka,r and correction coefficients determined using the American Association of Physicists in Medicine Task Group methodology is reported across a similar range of X-ray beam spectra.
Conclusion: The content of this research provides the necessary foundation for determining radiation dose at depth in soft tissue from state-of-the-art fluoroscopes. The results from this research can be used to assess dose at depth in soft tissue from fluoroscopically guided interventions, to determine fetal dosimetry from fluoroscopically guided interventions, and to validate dose modeling software.
Included in Bioimaging and Biomedical Optics Commons. Enter search terms:. Links WSU Libraries. Digital Commons.Quality of X-Ray Beams In Chapter 5we described an x-ray beam in terms of photon fluence and energy fluence. Such a description requires the knowledge of the number and energy of the photons in the beam. In this chapter, we will characterize an x-ray beam in terms of its ability to penetrate materials of known composition. The penetrating ability of the radiation is often described as the quality of the radiation.
An ideal way to describe the quality of an x-ray beam is to specify its spectral distribution, that is, energy fluence in each energy interval as shown in Figure 3. However, spectral distributions are difficult to measure and, furthermore, such a complete specification of the beam quality is not necessary in most clinical situations.
Since the biologic effects of x-rays are not very sensitive to the quality of the beam, in radiotherapy one is interested primarily in the penetration of the beam into the patient rather than its detailed energy spectrum.
Thus, a crude but simpler specification of the beam quality is often used, namely the half-value layer. Because all x-ray beams produced by radiation generators are heterogeneous in energy i. In the case of low-energy x-ray beams below megavoltage rangeit is customary to describe the quality in terms of HVL together with kVp, although HVL alone is adequate for most clinical applications.
On the other hand, in the megavoltage x-ray range, the quality is specified by the peak energy and rarely by the HVL. The reason for this convention is that in the megavoltage range the beam is so heavily filtered through the transmission-type target and the flattening filter that any additional filtration does not significantly alter the beam quality or its HVL.
The average energy of such a beam is approximately one-third of the peak energy. The x-rays produced by an x-ray generator show a continuous distribution of energies of bremsstrahlung photons on which are superimposed discrete lines of characteristic radiation Fig. The curve A in Figure 7. This distribution includes the effects of attenuation in the glass envelope of the x-ray tube, the surrounding oil, and the exit window of the tube housing as well.
This so-called inherent filtration is equivalent to approximately 1-mm Al in most x-ray tubes. The K-characteristic x-rays produced in the tungsten target possess discrete energies between 58 and 69 keV Table 3. Other emission lines of tungsten, however, have much lower energies and are not shown in Figure 7. Figure 7. Schematic graph showing changes in spectral distribution of a kVp x-ray beam with various filters. The energy fluence of the K lines of tungsten can be preferentially reduced using a tin filter.
Because the K absorption edge of tin is at about However, lower-energy photons cannot eject the K electrons. As seen in curve B of Figure 7. Because the L absorption edge of tin is only 4. In addition to the above effects, tin produces its own characteristic radiation by the photoelectric process involving the K shell, and these lines are superimposed on the spectrum below the tin absorption edge.
To absorb preferentially the energy fluence below the K edge of tin, including the characteristic x-rays of tin, a copper filter is quite efficient. The K edge of copper is at 9 keV, and therefore, the photons below 29 keV are strongly absorbed by the copper filter as seen in curve C of Figure 7. The very-low-energy characteristic x-rays produced by copper can be effectively absorbed by adding an aluminum filter next to the copper filter.
Combination filters containing plates of tin, copper, and aluminum have been designed to increase the resulting HVL of the orthovoltage beams without reducing the beam intensity to unacceptably low values.
Such filters are called Thoraeus filters 1 and are described in Table 7. It is important that the combination filters be arranged in the proper order, with the highest-atomic-number material nearest the x-ray target. Thus, a Thoraeus filter is inserted with tin facing the x-ray tube and the aluminum facing the patient, with the copper sandwiched between the tin and the aluminum plates. In the diagnostic and superficial x-ray energy range Section 4.X-rays are a form of electromagnetic radiation; their basic physical properties are identical to those of the more familiar components of the electromagnetic spectrum—visible lightinfrared radiationand ultraviolet radiation.
As with other forms of electromagnetic radiationX-rays can be described as coupled waves of electric and magnetic fields traveling at the speed of light aboutkm, ormiles, per second. Their characteristic wavelengths and frequencies can be demonstrated and measured through the interference effects that result from the overlap of two or more waves in space.
X-rays also exhibit particle-like properties; they can be described as a flow of photons carrying discrete amounts of energy and momentum. This dual nature is a property of all forms of radiation and matter and is comprehensively described by the theory of quantum mechanics. X-rays are distinguished by their very short wavelengths, typically 1, times shorter than the wavelengths of visible light.
Because of this, and because of the practical difficulties of producing and detecting the new form of radiation, the nature of X-rays was only gradually unraveled in the early decades of the 20th century. Polarization refers to the orientation of the oscillations in a transverse wave; all electromagnetic waves are transverse oscillations of electric and magnetic fields. The very short wavelengths of X-rays, hinted at in early diffraction studies in which the rays were passed through narrow slits, was firmly established in by the pioneering work of the German physicist Max von Laue and his students Walter Friedrich and Paul Knipping.
Laue suggested that the ordered arrangements of atoms in crystals could serve as natural three-dimensional diffraction gratings. These experiments demonstrated that X-rays have wavelengths of about 1 angstrom and confirmed that the atoms in crystals are arranged in regular structures.
In the following year, the British physicist William Lawrence Bragg devised a particularly simple model of the scattering of X-rays from the parallel layers of atoms in a crystal.
The Bragg law shows how the angles at which X-rays are most efficiently diffracted from a crystal are related to the X-ray wavelength and the distance between the layers of atoms.
The pair used their X-ray spectrometer in making seminal studies of both the distribution of wavelengths in X-ray beams and the crystal structures of many common solids—an achievement for which they shared the Nobel Prize for Physics in In the early s, experimental studies of the scattering of X-rays from solids played a key role in establishing the particle nature of electromagnetic radiation.
Further verification came in when American physicist Arthur Compton successfully treated the scattering of X-rays from the atoms in a solid as a set of collisions between X-ray photons and the loosely bound outer electrons of the atoms.
Adapting the relation between momentum and energy for a classical electromagnetic wave to an individual photon, Compton used conservation of energy and conservation of momentum arguments to derive an expression for the wavelength shift of scattered X-rays as a function of their scattering angle.
In the so-called Compton effecta colliding photon transfers some of its energy and momentum to an electron, which recoils. The scattered photon must thus have less energy and momentum than the incoming photon, resulting in scattered X-rays of slightly lower frequency and longer wavelength.
The defining characteristics of X-rays—their ability to penetrate optically opaque materials, their wavelengths of atomic dimension, the high energy of individual X-ray photons—lead to a wide range of industrial, medical, and scientific applications. Specialized X-ray sources, detectors, and analysis techniques have been developed to address a range of questions from the study of the interactions of the simplest molecules to the structure of the human brain.
X-ray images of the body are an indispensable diagnostic tool in modern medicine. Medical imaging allows for the nonintrusive detection of dental cavities, bone fractures, foreign objects, and diseased conditions such as cancer. Standard X-ray images easily differentiate between bone and soft tissue; additional contrast between different areas of soft tissue is afforded by the injection of a contrast medium—a liquid or gas that is comparatively opaque to X-rays see diagnostic imaging.
In the s a powerful new X-ray imaging technique, computed tomography CTwas developed.
Quality of X-Ray Beams
Now in widespread use, CT scans produce detailed high-resolution cross-sectional images of internal organs and structures; they are far more sensitive to small density variations than conventional X-ray images.
As with other forms of ionizing radiationX-rays cause biochemical changes in living cells. A high-energy X-ray photon deposits its energy by liberating electrons from atoms and molecules.Chapter 22 Factors affecting X-ray beam quality and quantity. The quantity of radiation in an X-ray beam is a measure of the number of photons in the beam.
The terms quantity and exposure are often interchanged in radiography as the higher the quantity or amount of radiation, the greater the exposure to a structure. In fact, probably the simplest method of comparing the quantity of two beams of radiation is to compare the exposure received by a structure. As we shall see in Chapter 27, the exposure is measured using the unit of air kerma.
As the quantity of radiation increases, so does the intensity of the beam. The quality of a beam of X-rays is a measure of its penetrating power. As we saw in Section In Sections Although the beam of X-rays from the tube is not monochromatic, but has a continuous spectrum over a wide range of energies, the half-value layer is a useful way of comparing the penetrating power of X-ray beams.
However, changing the quality of the radiation beam also affects the intensity of the beam. For a given quantity of radiation, the higher the quality of the radiation, the greater the intensity of the radiation beam. The intensity of a beam of X radiation is defined as the total amount of energy — measured at right angles to the direction of the beam — passing through unit area in unit time.
Although measured in units of joules per metre squared per second, in radiography we tend to use one of its effects — the ionization of air or of air kerma — as a measurement of radiation beam intensity.
In Chapter 21 we considered the mechanisms by which X-rays were produced at the anode of the X-ray tube. Before we look at this in any more detail, it is first important to ensure that we understand the meaning of the terms quantityquality and intensity as applied to a beam of X radiation.
If the current through the X-ray tube mA is, for example, doubled, the number of electrons flowing across the tube in unit time is doubled. If all the other factors remain unchanged, each electron will have the same chance of creating X-ray photons and so the number of photons of each energy produced per unit time will be doubled. If the mA is halved, the same argument can be used to show that the number of X-ray photons of each energy is also halved.
Thus we can say that the quantity of the X-ray beam per unit time or the beam intensity is directly proportional to the mA through the tube.18. Ion-Nuclear Interactions II — Bremsstrahlung, X-Ray Spectra, Cross Sections
Equation The effect on the X-ray beam of altering the mA is shown in Figure The maximum photon energy and the minimum photon energy are the same in each case and the average photon energy remains unaltered.
Figure Note that the quantity of the radiation changes — as shown by the alteration of the area under each curve — but the quality of the radiation is unaltered — as shown by the maximum photon energy and the peak photon energy being at the same energy for each graph. Thus we can say that the mA selected for an exposure affects the quantity of the X-ray beam but does not affect the quality of the beam — an increase in the mA will produce an increase in the quantity of radiation from the target.
The kVp across the X-ray tube influences the force of attraction experienced by an electron released by the filament as it moves towards the anode. Thus, if the kVp is increased, then the kinetic energy of the electron at the point when it starts to interact with the target will be increased. As we already discussed in Section Factors affecting X-ray beam quality and quantity. Chapter 22 Factors affecting X-ray beam quality and quantity Chapter contents Definitions The quantity of radiation in an X-ray beam is a measure of the number of photons in the beam.
Only gold members can continue reading. Log In or Register to continue. You may also need The radiographic image Interactions of X-rays with matter Principles of radiation dosimetry The inverse square law Exposure and timing circuits Mammography The diagnostic X-ray tube Capacitors. Tags: Principles and Applications of Radiological Physics.Filters are metal sheets placed in the x-ray beam between the window and the patient that are used to attenuate the low-energy soft x-ray photons from the spectrum.
Filtering is the removal of these low energy x-rays from the beam spectrum which would otherwise not contribute to image quality but would add to patient dose and scatter. If unfiltered these low-energy x-ray photons are generally absorbed by superficial structures of the body and contribute to the entrance surface dose ESD.
As they are absorbed by the superficial structures they contribute minimally to image formation. Using a filter reduces the ESD and to a lesser extent effective dose for the patient 1. The units of filtration are expressed in mm of aluminum equivalence mm Al eq.
Total filtration is the combined effect of inherent and added filtration, with US guidelines stating a minimum total filtration of 2.
The added filtration component is customized filter thickness, type of metal for individual examinations and procedures e. Beryllium is commonly used in mammography which use low-energy photons as it provides very little filtration.
Other types of x-ray generally use aluminum, copper or tin. Filtration reduces x-ray intensity quantity and quality shape of beam spectrumbut not the maximum energy of the x-ray beam spectrum. The change in the shape of beam spectrum with filtration is referred to as beam hardening. This is due to the loss of lower energy photons from a polychromatic beam. The average x-ray energy is increased and becomes more penetrating 6. Please Note: You can also scroll through stacks with your mouse wheel or the keyboard arrow keys.
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Features of X-ray Spectrum
Leonie Munro, World Health Organization. Terri L. Radiographic Imaging and Exposure. ISBN: 4. Peter Hertrich.
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