Effective Linear Attenuation Coefficient Research Articles

Synthesis and Gamma-ray Shielding Efficiency of Borosilicate Glasses Doped with Zinc Oxide: Comparative Study

This study examined the suitability of several glass compositions as a gamma-ray shielding substance. The compositions tested were of varying ZnO concentrations, specifically (60-x) B2O3—10Na2O—15SiO2—5Al2O3—(x + 10)ZnO (where X = 5, 10, 15 and 20 mol%). Measurements were performed at energy levels of 0.6642, 1.1776, and 1.3343 MeV radiated from Cs137 and Co60 point sources along with a scintillation detector [NaI(TL)]. We investigated the critical properties related to gamma radiation shielding, determining the effective atomic number (Zeff), electron density (Nel), half-value layer (HVL), linear attenuation (μ) and mass attenuation (μm) coefficients, and mean free path (λ). Our results show that the glasses under examination get denser (from 2.12 to 2.77 g/cm3) as the Zn concentration rises from 15 to 35 mol %. In addition, all glass compositions provide adequate protection against gamma radiation at the specified energy levels. The values of µ went up from 0.157 to 0.214 cm−1 (0.6642 MeV), from 0.119 to 0.160 cm−1 (1.1776 MeV), and from 0.114 to 0.151 (1.3343 MeV). For samples B1 and B4, the observed HVL values dropped from 4.41, 5.84, and 6.12 cm to 3.21, 4.31, and 4.61 cm at 0.6642, 1.1736, and 1.3343 MeV, respectively. Among the materials tested, prepared glasses show higher shielding capacity compared to regularly used glass and concrete samples. The study highlights these glass compositions' potential as practical materials that can shield gamma radiation.

Physical, Mechanical, and ionizing radiation shielding properties of 10PbO–10Na2O-(80-x)B2O3-xBaO glasses

This research explored the mechanical, physical, and ionizing radiation shielding properties of 10PbO–10Na2O-(80-x)B2O3-xBaO glass samples, where x = 10, 15, 20, and 25. The conventional melt-quench technique was employed to prepare the samples. The elastic moduli were investigated using the Makishima–Mackenzie model. At the same time, the radiation shielding properties involved a comprehensive analysis of the effective atomic number, linear attenuation and mass attenuation coefficients, half-value and tenth-value layers, radiation protection efficiency, and transmission factors, as well as the buildup factors for different mean-free paths (mfp). The impact of BaO (mol%) on the parameters mentioned above was investigated across a range of photon energies (0.015–15 MeV). In addition, the effect of BaO on the physical and mechanical properties of current glasses was studied. The addition of BaO showed an inverse impact on mechanical and physical properties, gradually reducing the glass's stability. In contrast, adding BaO to the compound enhanced photon attenuation ability, which means the sample with 25% BaO had the optimum capacity for radiation shielding amongst all the prepared samples. Moreover, the results demonstrated the complex interplay of Compton scattering, pair production, and the photoelectric effect, influencing the attention of photons. This work provides beneficial intuition into designing and optimizing glass-based radiation shielding materials.

Development of a semi empirical calculation approach for the determination of percentage depth dose in water for higher energy photon beams using a medical linear accelerator

The development of a calculation approach to determine the Percentage Depth Dose (PDD) by manual calculation for medical linear accelerator of 6 MV and 15 MV photon beam energy. The equation to determine PDD can be divided into two components i.e., the primary component and the scatter component. To calculate the primary component, the linear attenuation coefficient needs to be calculated. The measurement of charge was taken at various depths and for different field sizes using 6 MV and 15 MV photon beams. To determine the linear attenuation coefficient, a graph of ln (MR) where, MR represents corrected meter reading was plotted against depth in cm. By plotting another graph of linear attenuation coefficient against field size, to determine the effective linear attenuation coefficient. The scattered component KS was graphically plotted against depth in cm and derived an equation for scatter component. The calculated PDD for 6 MV was found to be within 1 % difference and for 15 MV percentage difference within 3 %. It was found that numerically developed PDD values table for higher energy photon beam becomes valid and it can be utilized for the manual dose calculation.

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.

Investigation of mechanical properties, photons, neutrons, and charged particles shielding characteristics of Bi2O3/B2O3/SiO2 glasses

Mechanical properties, uncharged and charged particles shielding capacity of 60Bi2O3-(40-x) B2O3-xSiO2: x = 0 (S1), 10 (S2), 20 (S3), 30 (S4), and 40 (S5) mol% glasses have been investigated. The enhancement in Young’s, shear, and longitudinal elastic moduli and Poisson’s ratio of the denser Bi content of the S-glasses was confirmed via bond compression (B–C) and Makishima–Mackenzie (M–M) models. The trend order of the mass attenuation coefficient (MAC) is consistent with that of the mass density as (S1)MAC (S2)MFP > (S3)MFP > (S4)MFP > (S5)MFP. The maximum tenth value thickness (TVT) of the glasses was recorded at 4 MeV with values of 3.93, 3.79, 3.70, 3.67, and 3.60 cm for S1, S2, S3, S4, and S5, respectively. The trend of the effective atomic number (Zeff) directly follows the MAC. Both exposure and energy absorption buildup factors (EBUF and EABUF) were increased with photon energy and depth of penetration except at Bi absorption edges where spikes were seen. Comparing the effective linear attenuation coefficient (ELAC) of the glasses, it is affirmed that S5 has the greatest photon absorption coefficient for all the considered energy and depth. Therefore, the S-glasses are better photon absorber and will perform better in gamma radiation shielding in nuclear facilities compared to commercially available glass shields (RS360 and RS520) and a recently investigated glass matrix (TVM60). In addition, the glass system can thus be used for fast neutron absorber rather than ordinary concrete or water.

CT imaging of gold nanoparticles in a human-sized phantom.

IntroductionGold nanoparticles (AuNPs) are visualized and quantified in a human‐sized phantom with a clinical MDCT scanner.MethodsExperiments were conducted with AuNPs between 0.00171 and 200 mgAu/mL. CT images were acquired at 80, 100, 120, and 140 kVp in a 33‐cm phantom. Image contrast due to AuNPs was experimentally determined from regions of interest (ROIs) and effective linear attenuation coefficients were calculated from CT x‐ray spectra with consideration of tissue attenuation.ResultsThe typical 12‐bit dynamic range of CT images was exceeded for AuNPs at 150 mgAu/mL. A threshold concentration of 0.3–1.4 mgAu/mL was determined for human visualization in 1‐mm images at a typical diagnostic CTDIvol of 23.6 mGy. Optimal image contrast was also achieved at 120 kVp and verified by calculation.ConclusionsWe have shown that scanners capable of reconstructing images with extended Hounsfield scales are required for distinguishing any contrast differences above 150 mgAu/mL. We have also shown that AuNPs result in optimal image contrast at 120 kVp in a human‐sized phantom due to gold’s 80.7 keV k‐edge and the attenuation of x‐rays by tissue. Typical CT contrast agents, like iodine, require the use of lower kVps for optimal visualization, but lower kVps are more difficult to implement in the clinic because of elevated noise levels, elongated scan times, and/or beam‐hardening artifacts. This indicates another significant advantage of AuNPs over iodine not yet discussed in the literature.

Comparative analysis of the transmission properties of tissue equivalent materials

Phantom objects have as main requirement to have the effective atomic number and linear attenuation coefficient approximately equal to the human tissue to be simulated. The present work aims to characterize samples of materials radiologically equivalent to water for dose studies in patients in the diagnostic energy range. Water was chosen as reference material representing human tissue, which is composed mostly of it. A set of samples was formulated and submitted to radiation transmission tests in four different values of tension applied to an X-ray tube. Mass densities of the samples were evaluated using the Arquimedes method. The samples were identified as A, B, C and D. By transmission curves, it was possible to estimate the samples transmission factors corresponding to the water transmission factor for different thicknesses. Moreover, the thicknesses of samples equivalent to water thickness for different values of transmission factor were also evaluated. All the samples densities were bigger than the density of water. For the same thickness of water and the samples, the radiation transmission of the developed materials are in better agreement for thicknesses of 10 mm and 30 mm. The lowest percentage difference between the water transmission and the transmission of any of the samples obtained was approximately 0.6% for the sample A in the thickness of 30 mm under voltage of 60 kV. The correspondence between the transmission factors and the thicknesses showed that the compounds studied in this work are potential materials to develop phantoms that simulate the transmission properties of human tissue.

VALIDATION OF A BEAMNRC MONTE CARLO SIMULATION OF A BROAD BEAM DIAGNOSTIC X-RAY UNIT.

A BEAMnrc Monte Carlo simulation of a diagnostic X-ray unit in a broad beam geometry intended for the derivation of effective linear attenuation coefficients was validated against measurements made on the X-ray unit on which the simulation was based. The validation process assessed the size of the beam, the first and second half value layer, the variation in kerma with anode-heel effect and the accuracy of values of effective linear attenuation coefficient for water and solid water attenuators. The agreement between the simulated and measured results for all tests was consistently within the experimental uncertainty for the measurements. The average deviation between values of effective linear attenuation coefficient for simulated and measured results is 3.8%, with the highest individual deviation 7.1%. The simulation can be used to produce values of effective linear attenuation coefficient for a range of kVp, field size and attenuator thickness that are close to those measured.

Density scaling of phantom materials for a 3D dose verification system.

In this study, the optimum density scaling factors of phantom materials for a commercially available three‐dimensional (3D) dose verification system (Delta4) were investigated in order to improve the accuracy of the calculated dose distributions in the phantom materials. At field sizes of 10 × 10 and 5 × 5 cm2 with the same geometry, tissue‐phantom ratios (TPRs) in water, polymethyl methacrylate (PMMA), and Plastic Water Diagnostic Therapy (PWDT) were measured, and TPRs in various density scaling factors of water were calculated by Monte Carlo simulation, Adaptive Convolve (AdC, Pinnacle3), Collapsed Cone Convolution (CCC, RayStation), and AcurosXB (AXB, Eclipse). Effective linear attenuation coefficients (μ eff) were obtained from the TPRs. The ratios of μ eff in phantom and water ((μ eff)pl,water) were compared between the measurements and calculations. For each phantom material, the density scaling factor proposed in this study (DSF) was set to be the value providing a match between the calculated and measured (μ eff)pl,water. The optimum density scaling factor was verified through the comparison of the dose distributions measured by Delta4 and calculated with three different density scaling factors: the nominal physical density (PD), nominal relative electron density (ED), and DSF. Three plans were used for the verifications: a static field of 10 × 10 cm2 and two intensity modulated radiation therapy (IMRT) treatment plans. DSF were determined to be 1.13 for PMMA and 0.98 for PWDT. DSF for PMMA showed good agreement for AdC and CCC with 6 MV x ray, and AdC for 10 MV x ray. DSF for PWDT showed good agreement regardless of the dose calculation algorithms and x‐ray energy. DSF can be considered one of the references for the density scaling factor of Delta4 phantom materials and may help improve the accuracy of the IMRT dose verification using Delta4.

Determining paediatric patient thickness from a single digital radiograph-a proof of principle.

This work presents a proof of principle for a method of estimating the thickness of an attenuator from a single radiograph using the image, the exposure factors with which it was acquired and a priori knowledge of the characteristics of the X-ray unit and detector used for the exposure. It is intended this could be developed into a clinical tool to assist with paediatric patient dose audit, for which a measurement of patient size is required. The proof of principle used measured pixel value and effective linear attenuation coefficient to estimate the thickness of a Solid Water attenuator. The kerma at the detector was estimated using a measurement of pixel value on the image and measured detector calibrations. The initial kerma was estimated using a lookup table of measured output values. The effective linear attenuation coefficient was measured for Solid Water at varying kVp. 11 test images of known and varying thicknesses of Solid Water were acquired at 60, 70 and 81kVp. Estimates of attenuator thickness were made using the model and the results compared to the known thickness. Estimates of attenuator thickness made using the model differed from the known thickness by 3.8 mm (3.2%) on average, with a range of 0.5-10.8 mm(0.5-9%). A proof of principle is presented for a method of estimating the thickness of an attenuator using a single radiograph of the attenuator. The method has been shown to be accurate using a Solid Water attenuator, with a maximum difference between estimated and known attenuator thickness of 10.8 mm (9%). The method shows promise as a clinical tool for estimating abdominal paediatric patient thickness for paediatric patient dose audit, and is only contingent on the type of data routinely collected by Medical Physics departments. Advances in knowledge: A computational model has been created that is capable of accurately estimating the thickness of a uniform attenuator using only the radiographic image, the exposure factors with which it was acquired and a priori knowledge of the characteristics of the X-ray unit and detector used for the exposure.

A novel physical anthropomorphic breast phantom for 2D and 3D x-ray imaging.

Physical phantoms are central to the evaluation of 2D and 3D breast-imaging systems. Currently, available physical phantoms have limitations including unrealistic uniform background structure, large expense, or excessive fabrication time. The purpose of this work is to outline a method for rapidly creating realistic, inexpensive physical anthropomorphic phantoms for use in full-field digital mammography (FFDM) and digital breast tomosynthesis (DBT). The phantom was first modeled using analytical expressions and then discretized into voxels of a specified size. The interior of the breast was divided into glandular and adipose tissue classes using Voronoi segmentation, and additional structures like blood vessels, chest muscle, and ligaments were added. The physical phantom was then fabricated from the virtual model in a slice by slice fashion through inkjet printing, using parchment paper and a radiopaque ink containing 33% (I33% ) or 25% (I25% ) iohexol by volume. Three types of parchment paper (P1, P2, and P3) were examined. The phantom materials were characterized in terms of their effective linear attenuation coefficients (μeff ) using full-field digital mammography (FFDM) and their energy-dependent linear attenuation coefficients (μ(E)) using a spectroscopic energy discriminating detector system. The printing method was further validated on the basis of accuracy, print consistency, and the reproducibility of ink batches. The μeff of two types of parchment paper were close to that of adipose tissue, with μeff = 0.61 ± 0.05 cm-1 for P1, 0.61 ± 0.04 cm-1 for P2, and 0.57 ± 0.03 cm-1 for adipose tissue. The addition of the iodinated ink increased the effective attenuation to that of glandular tissue, with μeff = 0.89 ± 0.06 cm-1 for P1 + I25% and 0.94 ± 0.06 cm-1 for P1 + I33% compared to 0.90 ± 0.03 cm-1 for glandular tissue. Spectroscopic measurements showed a good match between the parchment paper and reference values for adipose and glandular tissues across photon energies. Good accuracy was found between the model and the printed phantom by comparing a FFDM of the virtual model simulated through Monte Carlo with a real FFDM of the fully printed phantom. High consistency was found over multiple prints, with 3% variability in mean ink signal across various samples. Reproducibility of ink consistency was very high with <1% variation signal from multiple batches of ink. Imaging of the phantom using FFDM and DBT systems showed promising utility for 2D and 3D imaging. A novel, realistic breast phantom can be created using an analytically defined breast model and readily available materials. The work provides a method to fabricate any virtual phantom in a manner that is accurate, inexpensive, easily accessible, and can be made with different materials or breast models.

SU‐F‐SPS‐06: Implementation of a Back‐Projection Algorithm for 2D in Vivo Dosimetry with An EPID System

Purpose:To implement a back‐projection algorithm for 2D dose reconstructions for in vivo dosimetry in radiation therapy using an Electronic Portal Imaging Device (EPID) based on amorphous silicon.Methods:An EPID system was used to calculate dose‐response function, pixel sensitivity map, exponential scatter kernels and beam hardenig correction for the back‐projection algorithm. All measurements were done with a 6 MV beam. A 2D dose reconstruction for an irradiated water phantom (30×30×30 cm3) was done to verify the algorithm implementation. Gamma index evaluation between the 2D reconstructed dose and the calculated with a treatment planning system (TPS) was done.Results:A linear fit was found for the dose‐response function. The pixel sensitivity map has a radial symmetry and was calculated with a profile of the pixel sensitivity variation. The parameters for the scatter kernels were determined only for a 6 MV beam. The primary dose was estimated applying the scatter kernel within EPID and scatter kernel within the patient. The beam hardening coefficient is σBH= 3.788×10−4 cm2 and the effective linear attenuation coefficient is µAC= 0.06084 cm−1. The 95% of points evaluated had γ values not longer than the unity, with gamma criteria of ΔD = 3% and Δd = 3 mm, and within the 50% isodose surface.Conclusion:The use of EPID systems proved to be a fast tool for in vivo dosimetry, but the implementation is more complex that the elaborated for pre‐treatment dose verification, therefore, a simplest method must be investigated. The accuracy of this method should be improved modifying the algorithm in order to compare lower isodose curves.

A brachytherapy photon radiation quality index QBT for probe-type dosimetry

IntroductionIn photon brachytherapy (BT), experimental dosimetry is needed to verify treatment plans if planning algorithms neglect varying attenuation, absorption or scattering conditions. The detector’s response is energy dependent, including the detector material to water dose ratio and the intrinsic mechanisms. The local mean photon energy E¯(r) must be known or another equivalent energy quality parameter used. We propose the brachytherapy photon radiation quality indexQBT(E¯), to characterize the photon radiation quality in view of measurements of distributions of the absorbed dose to water, Dw, around BT sources. Materials and methodsWhile the external photon beam radiotherapy (EBRT) radiation quality index QEBRT(E¯)=TPR1020(E¯) is not applicable to BT, the authors have applied a novel energy dependent parameter, called brachytherapy photon radiation quality index, defined as QBT(E¯)=Dprim(r=2cm,θ0=90°)/Dprim(r0=1cm,θ0=90°), utilizing precise primary absorbed dose data, Dprim, from source reference databases, without additional MC-calculations. Results and discussionFor BT photon sources used clinically, QBT(E¯) enables to determine the effective mean linear attenuation coefficient μ¯(E) and thus the effective energy of the primary photons Eprimeff(r0,θ0) at the TG-43 reference position Pref(r0=1cm,θ0=90°), being close to the mean total photon energy E¯tot(r0,θ0). If one has calibrated detectors, published E¯tot(r) and the BT radiation quality correction factor kQ,Q0BT(E¯,r,θ) for different BT radiation qualities Q and Q0, the detector’s response can be determined and Dw(r,θ) measured in the vicinity of BT photon sources. ConclusionsThis novel brachytherapy photon radiation quality indexQBT characterizes sufficiently accurate and precise the primary photon‘s penetration probability and scattering potential.

English

The effective linear attenuation coefficients and build-up factors for single shield of Al, Fe, Pb, and for multi-layer shield of Al-Pb, Al-Fe, Fe-Pb, Al-Fe-Pb as a function of shield thickness, atomic number, and order of the materials composing the shield are investigated for two photon energies of 0.662 MeV and 1.25 MeV. Two derived practical formulas to calculate the effective attenuation coefficient and build-up factor for multilayer shields are used. It is noticed that changing the order of the materials among the shield has no significant effect on the experimental result. Measurement agrees well with the trend of the suggested formulas for calculating the effective attenuation coefficient and the buildup factor. The linear attenuation coefficient is observed to have a strange dependency with the atomic number and photon energy. For single layer shield, the attenuation coefficient increases with decreasing atomic number at low photon energy and increasing with increasing atomic number at high photon energy.

Dosimetric measurements of an n-butyl cyanoacrylate embolization material for arteriovenous malformations.

The therapeutic regimen for cranial arteriovenous malformations often involves both stereotactic radiosurgery and endovascular embolization. Embolization agents may contain tantalum or other contrast agents to assist the neurointerventionalists, leading to concerns regarding the dosimetric effects of these agents. This study investigated dosimetric properties of n-butyl cyanoacrylate (n-BCA) plus lipiodol with and without tantalum powder. The embolization agents were provided cured from the manufacturer with and without added tantalum. Attenuation measurements were made for the samples and compared to the attenuation of a solid water substitute using a 6 MV photon beam. Effective linear attenuation coefficients (ELAC) were derived from attenuation measurements made using a portal imager and derived sample thickness maps projected in an identical geometry. Probable dosimetric errors for calculations in which the embolized regions are overridden with the properties of water were calculated using the ELAC values. Interface effects were investigated using a parallel plate ion chamber placed at set distances below fixed samples. Finally, Hounsfield units (HU) were measured using a stereotactic radiosurgery CT protocol, and more appropriate HU values were derived from the ELAC results and the CT scanner's HU calibration curve. The ELAC was 0.0516 ± 0.0063 cm(-1) and 0.0580 ± 0.0091 cm(-1) for n-BCA without and with tantalum, respectively, compared to 0.0487 ± 0.0009 cm(-1) for the water substitute. Dose calculations with the embolized region set to be water equivalent in the treatment planning system would result in errors of -0.29% and -0.93% per cm thickness of n-BCA without and with tantalum, respectively. Interface effects compared to water were small in magnitude and limited in distance for both embolization materials. CT values at 120 kVp were 2082 and 2358 HU for n-BCA without and with tantalum, respectively; dosimetrically appropriate HU values were estimated to be 79 and 199 HU, respectively. The dosimetric properties of the embolization agents are very close to those of water for a 6 MV beam. Therefore, treating the entire intracranial space as uniform in composition will result in less than 1% dosimetric error for n-BCA emboli smaller than 3.4 cm without added tantalum and n-BCA emboli smaller than 1.1 cm with added tantalum. Furthermore, when effective embolization can be achieved by the neurointerventionalist using n-BCA without tantalum, the dosimetric impact of overriding material properties will be lessened. However, due to the high attenuation of embolization agents with and without added tantalum for diagnostic energies, artifacts may occur that necessitate additional imaging to accurately identify the spatial extent of the region to be treated.

SU‐E‐T‐415: Dosimetric Measurements of An N‐Butyl Cyanoacrylate Embolization Material for Arteriovenous Malformations

Purpose: The therapeutic regimen for cranial arteriovenous malformations (AVMs) often involves both stereotactic radiosurgery and adjunct endovascular embolization. Embolization agents often contain radiopaque contrast to assist the neurointerventionalists, leading to concerns regarding the dosimetric effects of these contrast agents. This study investigated dosimetric properties of n‐butyl cyanoacrylate (n‐BCA) plus lipiodol (NPL) with and without tantalum powder. Methods: The NPL was provided cured from the manufacturer (Codman Trufill; Codman &amp; Shurtleff, Inc., Raynham, MA) with and without tantalum. Attenuation measurements were made for the samples with and without tantalum powder and compared to the attenuation of a water substitute using a 6MV photon beam. Effective linear attenuation coefficients (ELAC) were derived from the attenuation measurements and measured sample thicknesses. Interface effects were investigated using a parallel plate ion chamber placed at set distances below fixed samples. Finally, Hounsfield units were measured using our department's standard stereotactic radiosurgery CT protocol. Results: For a 3cm square field, the ELAC was 0.0428 1/cm and 0.0474 1/cm for NPL without and with tantalum respectively, compared to 0.0461 1/cm for the water substitute. Non‐density corrected dose calculations would Result in errors of −0.33% and 0.13% per cm thickness of NPL without and with tantalum, respectively. Interface effects compared to water were less than 1.3% for both embolization materials. CT values at 120 kVp were 2082 HU and 2358 HU for NPL without and with tantalum, respectively. Conclusion: The dosimetric properties of NPL are very close to those of water for therapeutic energies. Therefore, treating the entire intracranial space as uniform in composition will Result in typically less than 1% dosimetric errors. However, due to the high attenuation of both embolization agents for diagnostic energies, artifacts may occur that necessitate MR imaging to accurately identify the spatial extent of the region to be treated.

SU‐C‐116‐02: Volumetric Dose Deposition in the Breast Using Real‐Time Dosimetry

Purpose: To empirically determine the angular dose distribution to a breast in a digital breast tomosythesis and mammography system using real‐time dosimetry technology. Methods: Three breast phantoms, constructed from polyethylene to simulate adipose tissue, were fabricated based on ninety cranio‐caudal mammography patients. The smallest (3.2 cm), average (5.1 cm), and largest (7.0 cm) breast thickness matched the measured breast shape using 13 mm polyethylene sheets. Technique factors, which matched the automatic settings in both tomo and mammo were used. Phantoms were designed to be modular allowing a dose probe to be placed in various heights and depths. A total of 390 signal trains, comprised of 15‐individual pulses (one for each angle) in tomo‐mode and a single pulse for mammo, were collected using a real‐time air ionization chamber (AccuGold, Radcal, Monrovia, CA). The signal train was integrated to generate a dose value at each location. This data was then used to generate a dynamic model of cumulative dose deposition as a function of x‐ray tube angle in tomo and mammo modes. Additionally, the effective linear attenuation coefficient for each energy was calculated. Using a look up table for the linear attenuation of polyethylene, the effective energy was calculated. Results: The dose deposition decreases from the compression paddle to the detector. Cumulative dose from tomo scan was comparable to that of mammo; differences in cumulative dose increased with phantom size. The effective energy for tomo at 28, 31 and 35 kVp with Al filter was calculated to be 19.7, 21.7 and 25 kV respectively. For mammo at 26, 29 (Rh filter) and 30 kV (Ag filter) was found to be19.1, 20.4 and 23.7 respectively. Conclusion: The volumetric dose deposition in Hologics dBT system shows angular dependence as a function of angle in tomo mode. NIH Grants

A solid iodinated phantom material for use in tomographic x‐ray imaging

Iodinated phantoms are of value in x-ray imaging for quality control measurements, system calibration, and for use in the research setting; however, the liquid phantoms that are most often used have several limitations including variability between repeated dilutions, inhomogeneities from air bubbles or precipitants, and long set up times. Although suitable materials have been investigated for projection radiography, quantitative measurements of contrast enhancement in computed tomography (CT) have become increasingly important in the clinic, and a need exists for a durable and reproducible iodinated phantom material. In this work, the authors describe a solid radiographic phantom material that has an accurately known concentration of iodine distributed uniformly throughout its volume and that has stable properties over time. This material can be molded or machined into a desired shape to create a test object or for use in an anthropomorphic phantom. Two sets of calibration phantoms were produced with a clinically relevant range of iodine concentrations. Measurements were made on these phantoms to characterize the material properties in terms of accuracy of iodine concentration, radiographic uniformity, temporal stability of x-ray attenuation, and manufacturing repeatability. Experimentally measured linear x-ray attenuation coefficients were compared to those predicted by a theoretical model. The uniformity of the iodine distribution in the material was assessed by measuring image intensity variation, both in projection images and in reconstructed CT volumes. The reproducibility of manufacture was estimated on a set of independently produced samples. A longitudinal study was performed to assess the stability of the material x-ray characteristics over time by making measurements at 6 month intervals. Good agreement was seen between the experimental measurements of effective attenuation and the theoretically predicted values. It is estimated that a desired iodine concentration could be produced to within 0.04 mg/ml. Comparison of the measured effective linear iodine attenuation coefficients of eight 1.0 mg/ml samples indicated a manufacturing reproducibility of +/-0.03 mg/ml iodine. Variations in uniformity across each of the samples were on the order of image intensity fluctuations (sigma). No inhomogeneities due to mixing or settling were apparent. An analysis of longitudinal data collected for both calibration sets revealed no perceptible change in radiographic properties over the first 6 months after manufacture, nor over a subsequent 1.5 yr period from 1 yr postmanufacture onward. The uniformity, stability, and precision of this iodinated material suggest that it is suitable for use in accurate calibration tools for contrast tomographic imaging.

Influence of extremely low energy radiation on artificial tissue: Effects on image quality and superficial dose

The design and slicing technique of artificial soft tissue are presented. Artificial soft tissue has optical penetration properties similar to biological tissues. The soft tissues are made of agar dissolved in water as a transparent tissue (control) incorporated with scatter materials such as polystyrene microspheres and absorbers such as artificial dairy substitute, coffee mate (Carnation Co.). The radiation's interaction with 20 and 40 keV X-ray, and visible light (400–800 nm) with different types of tissue phantoms has been investigated. The half value layer (HVL), attenuation coefficient, energy density and penetration depth through the artificial tissues has been calculated. X-ray radiation depth show significant reduction in soft tissue incorporated with polystyrene microspheres. At extremely low energy (E), the half value layer decreases with increasing the energy, while the attenuation coefficient increase. The calculated values of the half value layers are in very good agreement with experimental results. The calculated values of effective linear attenuation coefficient, are found to be µeff(0.22–0.42). Significant reduction in superficial dose with clear image is found with 10 mm soft tissue filter used. These results suggests: possible enhancement in diagnostic imaging and reduction in excess dose to patients; artificial soft tissue can be used as filter substitute.

Influence of extremely low energy radiation on artificial tissue: Effects on image quality and superficial dose

The design and slicing technique of artificial soft tissue are presented. Artificial soft tissue has optical penetration properties similar to biological tissues. The soft tissues are made of agar dissolved in water as a transparent tissue (control) in- corporated with scatter materials such as polystyrene microspheres and absorbers such as artificial dairy substitute, coffee mate (Carnation Co.). The radiation's interaction with 20 and 40 keV X-ray, and visible light (400-800 nm) with different types of tissue phantoms has been investigated. The half value layer (HVL), attenuation coefficient, energy density and penetration depth through the artificial tissues has been calculated. X-ray radiation depth show significant reduction in soft tissue incorporated with polystyrene microspheres. At extremely low energy (E), the half value layer decreases with increasing the energy, while the attenuation coefficient increase. The calculated values of the half value layers are in very good agreement with experimental results. The calculated values of effective linear attenuation coefficient, are found to be μeff (0.22-0.42). Significant reduction in superficial dose with clear image is found with 10 mm soft tissue filter used. These results suggests: possible enhancement in diagnostic imaging and reduction in excess dose to patients; artificial soft tissue can be used as filter substitute.