Effective Mass Attenuation Coefficient Research Articles

Comparative X-ray Shielding Properties of Single-Layered and Multi-Layered Bi2O3/NR Composites: Simulation and Numerical Studies.

This work theoretically compared the X-ray attenuation capabilities in natural rubber (NR) composites containing bismuth oxide (Bi2O3) by determining the effects of multi-layered structures on the shielding properties of the composites using two different software packages (XCOM and PHITS). The shielding properties of the single-layered and multi-layered Bi2O3/NR composites investigated consisted of the transmission factor (I/I0), effective linear attenuation coefficient (µeff), effective mass attenuation coefficient (µm,eff), and effective half-value layer (HVLeff). The results, with good agreement between those obtained from XCOM and PHITS (with less than 5% differences), indicated that the three-layered NR composites (sample#4), with the layer arrangement of pristine NR (layer#1)-Bi2O3/NR (layer#2)-pristine NR (layer#3), had relatively higher X-ray shielding properties than either a single-layer or the other multi-layered structures for all X-ray energies investigated (50, 100, 150, and 200 keV) due to its relatively larger effective percentage by weight of Bi2O3 in the composites. Furthermore, by varying the Bi2O3 contents in the middle layer (layer#2) of sample#4 from 10 to 90 wt.%, the results revealed that the overall X-ray shielding properties of the NR composites were further enhanced with additional filler, as evidenced by the highest values of µeff and µm,eff and the lowest values of I/I0 and HVLeff observed in the 90 wt.% Bi2O3/NR composites. In addition, the recommended Bi2O3 contents for the actual production of three-layered Bi2O3/NR composites (the same layer structure as sample#4) were determined by finding the least Bi2O3 content that enabled the sample to attenuate incident X-rays with equal efficiency to that of a 0.5-mm lead sheet (with an effective lead equivalence of 0.5 mmPb). The results suggested that the recommended Bi2O3 contents in layer#2 were 82, 72, and 64 wt.% for the combined 6 mm, 9 mm, and 12 mm samples, respectively.

Dependence of the effective mass attenuation coefficient of gold nanoparticles on its radius

Purpose: Several investigations are being carried since the past decade to use gold nanoparticles’ (AuNP) suspensions as contrast agents (CA) for imaging in Computed Tomography. For this, the optimal size of AuNP has received considerable attention, which is addressed here. Material and methods: In this theoretical study, effective attenuation coefficient for a single spherical shaped AuNP is first calculated from the first principles, as a function of the nanoparticle radius 'r', with μ(E) being the attenuation coefficient of the material for a given energy E. This result is extended to derive a formula for the attenuation coefficient and mass attenuation coefficient of a suspension of AuNP. Results: It is seen that the effective mass attenuation coefficient of the nanoparticles is a decreasing function of α(E) = 2μ(E)r and falls inversely with α(E), for large values of α(E) ≫ 1, there being very little change for α ≤ 1. Conclusion: The paper shows that for nanoparticles, less than 100 nm in diameter the linear attenuation coefficient of the colloidal suspension has no dependence on the nanoparticles' size and depends only on the concentration of nanoparticle material present in the suspension.

Fabrication and Characterization of Bolus Material Using Propylene Glycol for Radiation Therapy

Introduction: This study aimed to evaluate the efficacy of a synthesized bolus in the reduction of damage to body tissues and the protection of the organ at risk (OAR) in radiotherapy application. Several properties of the synthesized bolus, including density, transmission factor, and effective mass attenuation coefficient, were investigated. Material and Methods: The materials used comprising of propylene glycol (PG), silicone rubber (SR), and aluminum (Al). The dimension of the synthesized bolus was measured using an acrylic case with a size of 11×11 cm² and thickness sizes of 0.5, 1, and 1.5 cm. Furthermore, the boluses were irradiated by linear accelerator with the photon beam energies of 6 and 10 MV, using linier accelerator (LINAC) Varian 2300ix. Results: In this research,the density of synthesized bolus was evaluated by mass per volume equation. The results showed that the density of bolus was similar to the density of tissue/water, fat, and air. . Furthermore the bolus with the composition of PG 24%, SR 8%, and Al 1.5% of all energies, transmission factors of 0.978 and 0.984, thickness of 1.5 cm, and effective mass attenuation coefficients of 0.0144 and 0.0107 cm²/g had the closest properties to the body tissues in terms of dosimetry characterization. Conclusion: The results revealed that the synthesized bolus could increase the percentage surface dose, reduce skin-sparing effect, and protect OAR. The findings indicated that the synthesized bolus had a potential application in clinical therapy.

Comparison of Dosimetry Characteristics from Some Bolus Materials for 6 and 10 MV Photons Beam Radiation Therapy

In radiation therapy, bolus material is often used for increased surface dose, compensate for surface irregularities and internal heterogeneities. Bolus has properties equivalent to water and soft tissue. In this study, the mixture of Silicone Rubber (SR) and Bismuth was used for bolus fabrication and then compared to commercial boluses such as Paraffin, Play-Doh, and Paraffin Wax. The study aims to evaluate the comparison of relative electron density (RED), effective mass attenuation coefficient, transmission factor, percentage of surface dose (PSD), and Percentage Depth Dose (PDD) for all boluses. The bolus was made with the size 11 × 11 × 0.5 cm3. Physical density of the synthesized bolus was assessed by computerized tomography (CT) Scanning. The results of the RED analysis for the mixture of Silicone Rubber (SR) and Bismuth, Paraffin, Play-Doh, and Paraffin Wax were 0.954; 0.743; 0.933; and 0.878, respectively. The values of RED for all boluses has a similar to water and soft tissue. These results prove that the bolus is equivalent to soft tissue density such as fat, breast, lungs, and liver. Furthermore, for other dosimetry tests such as transmission factors and attenuation coefficients using Linear Accelerator (LINAC) with photon energy sources 6 and 10 MV. In general, Percentage of surface dose at 6 MV is higher than 10 MV. The highest percentage of the surface dose was achieved by paraffin wax at 6 MV energy by 85%. For effective mass attenuation coefficient result, the highest is the mixture of silicone rubber and bismuth at -0.0030 cm2/g for 6 MV and Play-Doh at -0.0114 cm2/g for 10 MV.

Dosimetry analysis of homemade bolus using propylene glycol for photon MegaVoltage and electron radiation therapy

Bolus is widely used to protect and reduce irradiation in organ at risk in the process of radiotherapy. Generally, the bolus was made from polymer material due to had property is similar or equivalent to tissue. This study aimed to determine the density, transmission factor, effective mass attenuation coefficient on bolus with radiation of photons and electrons. The bolus material (B) was used Propylene Glycol (PG), Silicon Rubber (SR) and Aluminium Powder (Al), and had four types of bolus namely B - PG 24%, B - PG 24%; SR 8%, B - PG 24%; SR 8%; Al 0,5%, and B - PG 24%; SR 8%; Al 1,5% with dimensions of 11 × 11 cm and thickness of 1 and 1.5 cm. The bolus density is evaluated through the mass of each volume. The measured data revealed that all of the boluses have density values which are similar to tissue or water and air in the range from 0,864 - 1,202 g/cm3. For dosimetry testing, the bolus is irradiated using Linear Accelerator with 6 and 10 MV for photon source and 6 and 12 MeV for an electron source. The results showed that B - PG 24%; SR 8%; Al 1.5% for dosimetry testing both 6 and 10 MV photons obtained properties that resemble soft tissue. Meanwhile, for both dosimetry testing of 12 MeV electrons, the B - PG 24%; SR 8% with addition silicone rubber and aluminum have nature closest to soft tissue. All of the boluses that have been fabricated have properties similar to soft tissue for photon therapy whereas the addition of more aluminum making a bolus has features as a shield on the process of radiotherapy.

Evaluations of absorbed dose ratio factor of Al2O3 dosemeter in radiotherapy photon beams using cavity theory

The aim of the work was to evaluate the absorbed dose ratio factor f(md) of an Al(2)O(3) dosemeter to water in photon radiotherapy beams using cavity theory. Burlin theory was used for calculating of this ratio. The effective mass attenuation coefficient β was obtained by comparing Monte Carlo simulations in monoenergetic photon beams. The evaluations of the absorbed dose ratio factor f(md) were studied for Al(2)O(3) dosemeters of different sizes, which were placed at various depths of the water phantom in different radiation field sizes of Mohan's 6, 10 and 15-MV X-rays. Beyond the build-up region, the variation of f(md) increases by 0.25 % as the depth increases from 4 to 10 cm. The maximum variation due to different dosemeter sizes is 8.3 %. The difference in the f(md) due to different radiation field sizes is 1.5 %. The effect of the dosemeter size cannot be neglected. The difference in the f(md) due to the radiation field sizes of different beams would increase as the dosemeter size increases.

Thickness determination of SmCo films on silicon substrates utilizing X-ray diffraction

This paper presents a nondestructive measurement technique for the determination of the film thicknesses of Co and SmCo based magnetic films deposited by sputtering on single-crystal silicon (100) substrates. X-ray diffraction of Cu Kα radiation has been used to measure the intensity of the (400) reflection from bare silicon substrates and as attenuated by sputter coated Co and SmCo based films on Si substrates. A four-axis research diffractometer allowed the substrate orientation to be fine adjusted to maximize the (400) diffraction intensity. The thickness of SmCo based films was in a range from 0.05 to 5 μm. Co film thicknesses on Si could be measured to a few tens of nanometers. The accuracy of the thickness measurements depends on the effective mass attenuation coefficient of the film material. For the materials considered, the thicknesses determined by the X-ray attenuation method agree within at least several percent to values determined by other methods.

Depth Scaling of Solid Phantom for Intensity Modulated Radiotherapy Beams

To reduce the uncertainty of absorbed dose for high energy photon beams, water has been chosen as a reference material by the dosimetry protocols. However, solid phantoms are used as media for absolute dose verification of intensity modulated radiotherapy (IMRT). For the absorbed dose measurement, the fluence scaling factor is used for converting an ionization chamber reading in a solid phantom to absorbed dose to water. Furthermore the depth scaling factor is indispensable in determining the fluence scaling factor. For IMRT beams, a photon energy spectrum is varied by transmitting through a multileaf collimator and attenuating in media. However, the effects of spectral variations on depth scaling have not been clarified yet. In this study, variations of photon energy spectra were determined using the EGS Monte Carlo simulation. The depth scaling factors for commercially available solid phantoms were determined from effective mass attenuation coefficients using photon energy spectra. The results clarified the effect of spectral variation on the depth scaling and produced an accurate scaling method for IMRT beams.

C-5 Absolute Thickness Determination of SMCO Films on Silicon Substrates Utilizing X-ray Diffraction and Their Composition Measurements By EXRF

This paper presents a nondestructive measurement technique for the accurate and absolute determination of film thicknesses of Co and SmCo based magnetic films deposited by sputtering on single crystal Silicon (100) substrates. X-Ray diffraction of Cu K radiation has been used to measure the intensity of the (400) reflection from bare silicon substrates and as attenuated by sputter coated Co and SmCo based films on Si substrates. A 4-axis research diffractometer allowed the substrate orientation to be fine adjusted to maximize the (400) diffraction intensity. The absolute thickness of SmCo based films was in a range from 0.05 to 5 Co film thicknesses on Si could be measured to a few tens of nanometers. The absolute accuracy of the thickness measurements depend on the effective mass attenuation coefficient of the film material. For the materials considered, thicknesses determined by the X-Ray attenuation method agree within at least several percent to values determined by other methods.

Dosimetric characteristics of a cubic‐block‐piled compensator for intensity‐modulated radiation therapy in the Pinnacle radiotherapy treatment planning system

We examined the dose distributions generated by Pinnacle3 (Philips Radiation Oncology Systems, Milpitas, CA) for intensity‐modulated radiotherapy (IMRT) plans using a cubic‐block‐piled compensator as the intensity modulator for 4‐MV and 10‐MV photon beams. The Pinnacle treatment planning system (TPS) uses an algorithm in which only the physical density of the absorber is required for calculating the characteristics of the modulator. The intensity modulator consists of cubic blocks (attenuator) of a tungsten alloy, plus cubic blocks of polyethylene resin foam that fill the spaces between the attenuator blocks and polymethyl methacrylate (PMMA) boards that act as the platform for the modulator. By measuring the transmission for various thicknesses of attenuator and by deriving values for the total physical density of the modulator, we determined the optimal effective density by comparing the curves fitted for the actual transmission data with the transmission calculated by the TPS. Using these effective densities, we examined the accuracy of Pinnacle3 for dose profiles of specific geometric patterns. The levels of consistency between the measurements and the calculations were within a tolerance of 3% of the dose difference and had a 3‐mm distance to agreement for the ladder‐, stairstep‐, and pyramid‐shaped test patterns, except in the high dose gradient region. In this modulator assembly, leakage occurred from the slits between the cubic blocks. This leakage was about 1.6% at maximum, and its influence on dose distribution was not crucial. In the TPS, in which physical density was the only user‐controllable parameter, we used the effective density of the absorber deduced from the effective mass attenuation coefficient. We conclude that the intensity modulation compensator system, together with a piled cubic attenuator, is clinically applicable, with an acceptable tolerance level. For the intensity map of the IMRT plan, measurements in treatment fields met 3% and 3‐mm criteria, excluding some regions of high gradient, which had a discrepancy of less than 5% and 4 mm.PACS numbers: 87.53.Mr, 87.53.Tf

Attenuation correction in quantitative SPECT ofcerebral blood flow: a Monte Carlo study

Monte Carlo simulation has been used to produce projections from a voxel-basedbrain phantom, simulating a 99mTc-HMPAO single photon emission computedtomography (SPECT) brain investigation. For comparison, projections free fromthe effects of attenuation and scattering were also simulated, giving idealtransaxial images after reconstruction. Three methods of attenuationcorrection were studied: (a) a pre-processing method, (b) a post-processinguniform method and (c) a post-processing non-uniform method using a densitymap. The accuracy of these methods was estimated by comparison of thereconstructed images with the ideal images using the normalized mean squareerror, NMSE, and quantitative values of the regional cerebral blood flow,rCBF. A minimum NMSE was achieved for the effective linear attenuationcoefficient µeff = 0.07 (0.09) cm-1 for the uniformpre method, the effectivemass attenuation coefficient µeff/ρ = 0.08 (0.10) cm2 g-1 for the uniformpostmethod and µeff/ρ = 0.12 (0.13) cm2 g-1 for the non-uniformpost method.Values in parentheses represent the case of dual-window scatter correction.The non-uniformpost method performed better, as measured by the NMSE, bothwith and without scatter correction. Furthermore, the non-uniformpost methodgave, on average, more accurate rCBF values. Although the difference in rCBFaccuracy was small between the various methods, the same method should be usedfor patient studies as for the reference material.

Modified general cavity theory applied to the calculation of gamma dose in 60Co thermoluminescence dosimetry

Burlin's general cavity theory for intermediate sized cavities incorporated two weighting factors: d, the average reduction in the electron fluence from the medium inside the cavity, and 1-d, the average fractional build-up to equilibrium of the cavity-generated electron spectrum-both calculated for an average path length g of electrons crossing the cavity. A new weighting factor d' has been introduced expressing the fact that average path length for medium- and cavity-generated electrons are not equal and this leads to a modified general cavity expression. The new expression is applied to 60Co thermoluminescence dosimetry experimental results of other workers. For LiF TLD in all the media agreement with experiment is improved. There is a significant dependence of the theoretical results on the effective mass attenuation coefficient, indicating the need for further studies.