Mass Energy Absorption Coefficients Research Articles

Natural polymer-based hydrogels as prospective tissue equivalent materials for radiation therapy and dosimetry.

Natural polymer-based hydrogels have been extensively employed in tissue engineering and biomedical applications, owing to their biodegradability and biocompatibility. In the present work, we have investigated the efficacy of hydrogels such as agarose, hyaluronan, gelatin, carrageenan, chitosan, sodium alginate and collagen as tissue equivalent materials with respect to photon and charged particle (electron, proton and alpha particle) interactions, for use in radiation therapy and dosimetry. Tissue equivalence has been investigated by computing photon mass energy absorption coefficient (μen/ρ), kinetic energy released per unit mass (KERMA), equivalent atomic number (Zeq) and energy absorption build-up factors (EABF) relative to human tissues (soft tissue, cortical bone, skeletal muscle, breast tissue, lung tissue, adipose tissue, skin tissue, brain) in the energy range of 0.015-15MeV. Ratio of effective atomic numbers (Zeff) have been examined for tissue-equivalence in the energy range of 10keV-1GeV for charged particle interactions. Analysis using standard theoretical formulations revealed that all the selected natural polymers can serve as good tissue equivalent materials with respect to all human tissues except cortical bone. Notably, sodium alginate, collagen and hyaluronan are found to have radiation interaction characteristics close to that of human tissues. These results would be useful in deciding on the suitability of a natural polymer hydrogel as tissue substitute in the desired energy range.

A simple software for swift computation of photon and charged particle interaction parameters: PAGEX

PAGEX is a compact and user-friendly cross-platform software developed for swift computation of photon (X-ray and γ-ray) and charged particle interaction parameters for various applications. It is designed based on well-established theoretical formulations and computational techniques integrating various Python packages to effectively calculate parameters such as partial/total photon interaction cross-sections and mass attenuation coefficients, charged particle mass stopping powers and cross-sections, effective atomic number and electron density, mass-energy absorption coefficient, KERMA and build-up factors over a wide energy range. This tool is capable of generating both tabular and graphical outputs which can be saved in any user desired format. PAGEX has been verified against other widely employed software and databases, demonstrating good agreement. This software which facilitates robust computation is freely available from the authors.

Evaluation of the physical, structural, thermal, and advanced radiation absorption characteristics of SiO2–Na2O–K2O–P2O5–CaO bioactive glasses

We report herein an evaluation of the physical, structural, thermal, advanced photon energy absorption, and fast neutron removal characteristics of a series of bioactive glasses having the compositions 20SiO2-7.5Na2O-7.5K2O-(65–x)P2O5-xCaO, where x = 2.5, 5.0, 7.5, and 10.0 mol.%. X-ray diffraction (XRD) patterns confirmed the amorphous nature of these phosphosilicate glass systems fabricated by the melt-quench technique. To confirm the in vitro bioactivity of the prepared glasses, powdered samples of each composition were compressed into pellets and then soaked in simulated body fluid (SBF) at 37 ± 0.5 °C for 28 days. Soaked samples were investigated by means of XRD, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS/EDX). Thermo-gravimetric and differential thermal analysis (TG-DTA) was applied to determine the glass transition temperature (Tg) and crystallization temperature (Tc) for each glass sample. Fourier-transform infrared (FTIR) measurements were performed in the range 4000–400 cm−1, and showed the bending and stretching motions of different groups and the presence of CO2 and OH− groups in the glasses. Radiation absorption properties, such as mass energy absorption coefficient (μen/ρ), kinetic energy released per unit mass (KERMA) relative to air (ҠR), and mean free path values have been obtained for the bioactive glasses and compared with those of registered 45S5 Bioglass®. The simultaneous variation of mass energy absorption and mass attenuation values with photon energy has been explored to visualize the difference between absorption and attenuation. Linear attenuation coefficients for the present glass samples have been measured at photon energies of 511, 662, 1173, and 1332 keV in narrow-beam transmission geometry, and were in good agreement with theoretical results (error < 2 %). Further, detailed comparative analysis of energy absorption build-up factor (EABF) values for the glass samples has been conducted using two software tools, namely Photon Shielding and Dosimetry (PSD) and EXABCal, as well as on the basis of equivalent atomic number (Zeq) and effective atomic number (Zeff). We also attempted to calculate effective removal cross-sections (∑R) in order to evaluate the neutron absorption performances of these glass samples. The present detailed analysis shows that glass sample S4 with 10 mol.% CaO exhibits the most promising radiation absorption properties, resembling those of 45S5 Bioglass®.

Air equivalence of some solid fluoropolymers in photon beams

Two fluoropolymers polyvinylidene fluoride (PVDF) and ethylene tetrafluoroethylene (ETFE), which differ only in chemical structure and have the same atomic composition, were evaluated for use in air simulation for phantom measurements in photon beams. Photon interaction was modelled using US-NIST datasets. In order to mimic the radiation properties of air with another material, values of the following quantities were chosen for comparison: total mass attenuation coefficients, mass-energy absorption coefficients, total electron mass stopping powers, mass collision stopping powers, and mass scattering powers. The calculated ratios of the corresponding coefficients or stopping powers between the material and air were the values of interest. The results for fluoropolymers were compared with other polymers commonly used in the manufacture of phantoms. The results show that in the photon energy range from 150 keV to 1 GeV both fluoropolymers exhibit excellent dosimetric properties slightly better than air equivalent plastic C552. The effect of a carbon-based filler added to the fluoropolymer to ensure the electrical conductivity of the resulting composite was also investigated. It has been found that the increased carbon-based filler content (up to 20 wt% of carbon) added to the fluoropolymer has a very small effect on the radiation properties of the composite.

A study of Type B uncertainties associated with the photoelectric effect in low-energy Monte Carlo simulations

Purpose. To estimate Type B uncertainties in absorbed-dose calculations arising from the different implementations in current state-of-the-art Monte Carlo (MC) codes of low-energy photon cross-sections (<200 keV). Methods. MC simulations are carried out using three codes widely used in the low-energy domain: PENELOPE-2018, EGSnrc, and MCNP. Three dosimetry-relevant quantities are considered: mass energy-absorption coefficients for water, air, graphite, and their respective ratios; absorbed dose; and photon-fluence spectra. The absorbed dose and the photon-fluence spectra are scored in a spherical water phantom of 15 cm radius. Benchmark simulations using similar cross-sections have been performed. The differences observed between these quantities when different cross-sections are considered are taken to be a good estimator for the corresponding Type B uncertainties. Results. A conservative Type B uncertainty for the absorbed dose (k = 2) of 1.2%–1.7% (<50 keV), 0.6%–1.2% (50–100 keV), and 0.3% (100–200 keV) is estimated. The photon-fluence spectrum does not present clinically relevant differences that merit considering additional Type B uncertainties except for energies below 25 keV, where a Type B uncertainty of 0.5% is obtained. Below 30 keV, mass energy-absorption coefficients show Type B uncertainties (k = 2) of about 1.5% (water and air), and 2% (graphite), diminishing in all materials for larger energies and reaching values about 1% (40–50 keV) and 0.5% (50–75 keV). With respect to their ratios, the only significant Type B uncertainties are observed in the case of the water-to-graphite ratio for energies below 30 keV, being about 0.7% (k = 2). Conclusions. In contrast with the intermediate (about 500 keV) or high (about 1 MeV) energy domains, Type B uncertainties due to the different cross-sections implementation cannot be considered subdominant with respect to Type A uncertainties or even to other sources of Type B uncertainties (tally volume averaging, manufacturing tolerances, etc). Therefore, the values reported here should be accommodated within the uncertainty budget in low-energy photon dosimetry studies.

Monte Carlo approach for calculation of mass energy absorption coefficients of some amino acids

This study offers a Monte Carlo alternative for computing mass energy absorption coefficients of any material through calculation of photon energy deposited per mass of the sample and the energy flux obtained inside a sample volume. This approach is applied in this study to evaluate mass energy absorption coefficients of some amino acids found in human body at twenty-eight different photon energies between 10 keV and 20 MeV. The simulations involved a pencil beam source modeled to emit a parallel beam of mono-energetic photons toward a 1 mean free path thick sample of rectangular parallelepiped geometry. All the components in the problem geometry were surrounded by a 100 cm vacuum sphere to avoid any interactions in materials other than the absorber itself. The results computed using the Monte Carlo radiation transport packages MCNP6.2 and GAMOS5.1 were checked against the theoretical values available from the tables of XMUDAT database. These comparisons indicate very good agreement and support the conclusion that Monte Carlo technique utilized in this fashion may be used as a computational tool for determining the mass energy absorption coefficients of any material whose data are not available in the literature.

Ionizing radiation and its considerations in imaging diagnosis: comparison of absorbed dose between cone beam computed tomography and multi-detector computed tomography in the head and neck

Introduction: The objective of this study was to compare the mean absorbed dose in patients undergoing head and neck examinations using two cone beam computed tomography (CBCT, Kodak and i-CAT) and one multi-detector computed tomography (MDCT). Methods: Three thermoluminescent dosimeters (TLDs), calibrated in air kerma, were positioned in 24 regions of the head and neck of a phantom simulating an average adult. The mean absorbed dose (mGy) values in these positions, for different organs and tissues, were obtained using correction factors, considering the ratio between the mass energy absorption coefficients of organ/tissue and air. Comparison between radiation doses in the most radiosensitive regions was done by calculating the ratio of these dose values, with propagated uncertainty. Results: The dose in all regions was significantly higher for MDCT when compared to CBCT. Concerning CBCT equipment, the Kodak device had a higher absorbed dose than the i-CAT for most of the regions tested. The uncertainty of the i-CAT was greater than that of the Kodak. Conclusion: Due to the considerable difference between absorbed doses, emphasizing the higher dose values obtained in MDCT, the dissemination of CBCT application in medicine is recommended, as well as further studies to broaden the criteria for use.

A parametric fitting technique for rapid determination of a skin-dose correction factor for angle of beam incidence during image-guided endovascular procedures.

Skin dose is dependent on the incident beam angle and corrections are needed for accurate estimation of the risk of deterministic effects of the skin. To obtain the angular correction factors (ACF's), EGSnrc Monte Carlo (MC) software was used to calculate the skin dose as a function of incident x-ray beam angle at the center of the field for beam energies from 60 to 120 kVp, field sizes from 5 to 15 cm, and thicknesses of Cu beam filters from 0.2 to 0.5 mm. All MC simulations used 3×1010 incident photons. The dose was averaged over a 1 mm depth on the entrance surface of a 40×40 cm by 20 cm thick water phantom and was then normalized to the incident primary dose which was calculated using NIST mass energy absorption coefficients and by integrating over the beam energy spectrum. The Matlab tool, 'cftool', was used to fit these normalized dose values to power law equations as a function of incident beam angle, with coefficients that were fit to polynomials as a function of kVp. Separate fitting was done for different beam sizes and beam filters. The skin dose values calculated using the ACF determined from the fitted functional formulas agreed with that calculated by MC with a mean absolute percentage error (MAPE) less than 3% over the entire range of incident angles and kVp values. This fitting technique allows an ACF to be quickly determined for accurate skin dose calculation.

Studies on partial and total photon interaction parameters in the energy range 1 keV–100 GeV of some synthetic polymers having medical applications

The effective atomic numbers and effective electron densities of some polymers having medical applications are determined for total as well as partial gamma ray interaction processes in the wide range of energies 1 keV to 100 GeV. Mass energy-absorption coefficient and effective atomic number corresponding to gamma ray energy absorption in these media are also estimated for the energy range of 1 keV–20 MeV. These parameters are found to vary with energy and chemical composition of the polymers. These variations are shown graphically and are discussed in detail. The estimated values are compared with experimental data, wherever available, and these show good agreement. The kerma relative to air of these polymers are also calculated for 1 keV-20 MeV. Kerma remains constant at unity from 200 keV to 10 MeV. The selected polymers have remarkable applications in the medical field and we expect that the data will be useful in medical domain.

A Monte Carlo study on the gamma-ray buildup factors for the linear sources embedded in a cylindrical shield

While the studies on the photon buildup factors for point gamma sources have been widely made, studies for linear gamma sources, for which the spent nuclear fuel rods and/or brachytherapy seeds could be a relatively good approximation, have become extremely scarce. Buildup factors for linear gamma sources are computed here by means of the MCNPX Monte Carlo code. The exposure buildup factors were calculated for isotropic linear gamma sources with different lengths (1, 10, and 100 cm) and also for different energies (0.1, 0.5, 1, 5, and 10 MeV) in a cylindrical concrete shield up to depths of 10 mean free paths. A number of 45 simulations were done to reach the appropriate results for the linear gamma sources and 5 more simulations were performed for point gamma sources to be compared with the linear sources of photons at the same energies. For validation, we calculated the total mass attenuation coefficients, mass energy absorption coefficients, and uncollided photon flux for some photon energy in concrete and we showed that the simulation results have a good agreement with NIST-XCOM database and theory. Finally, comparisons are shown for the exposure buildup factors of the linear source in terms of the gamma-rays energy, of the length of the linear source and of the cylindrical shield, which can be useful in the design of a suitable shield.

Calcium-based TLD materials for radiation applications

This study focused on radiation interaction parameters of four compounds of calcium which are the most common types of thermoluminescence dosimetry (TLD). Firstly, the mass attenuation coefficients (MAC, μ/ρ) and effective atomic numbers (Zeff) of calcium based-TLD materials such as CaSO4, CaF2, Ca5F(PO4)3 and CaCO3 were measured in the energy region 121.87–1408.01 keV. The values of MACs and Zeffs of CaSO4, CaF2, Ca5F(PO4)3 and CaCO3 were then theoretically calculated at same photon energies. Good agreements were observed between the experimental and theoretical results for MAC and Zeff values (diff. ≤ 8.17%). In addition, the mass energy absorption coefficients, Kerma relative to soft tissues, equivalent atomic number (Zeq), and buildup factors (energy absorption and exposure buildup factors; EABF, EBF) were theoretically calculated in the energy region 0.08–2 MeV. The results displayed significant changes in equivalent atomic number, such that these values increased with the increasing energy and after 1 MeV it generally decreased. CaCO3 was finally found the best tissue equivalent material because of fact that the values of Kerma and Zeff ratios were nearest to unity (1) among calcium-based TLD materials at the studied energies.

Quantitative proton radiation therapy dosimetry using the storage phosphor europium-doped potassium chloride.

To (a) characterize the fundamental optical and dosimetric properties of the storage phosphor europium-doped potassium chloride for quantitative proton dosimetry, and (b) investigate if its dose radiation response can be described by an analytic radiation transport model. Cylindrical KCl:Eu2+ dosimeters with dimensions of 6mm diameter and 1mm thickness were fabricated in-house. The dosimeters were irradiated using both a Mevion S250 passive scattering proton therapy system and a Varian Clinac iX linear accelerator. Photostimulated luminescence (PSL) emission spectra, excitation spectra, and luminescence lifetimes were measured for both proton and photon irradiations. Dosimetric properties including radiation hardness, dose linearity, signal stabilization, dose rate sensitivity, and energy dependence were studied using a laboratory optical reader after irradiations. The dosimeters were modeled using physical quantities including mass stopping powers in the storage phosphor and water for a given proton beam, and mass energy absorption coefficients and massing stopping powers in detector and water for a given photon beam. KCl:Eu2+ exhibited optical emission and stimulation peaks at 421 and 560nm, respectively, for both proton and photon irradiations, enabling postirradiation readouts using a visible light source while detecting the PSL using a photomultiplier tube. KCl:Eu2+ showed a linear response from 0 to 8Gy absorbed dose-to-water, a large dynamic range up to 60Gy, dose-rate independence measured from 83 to 500MU/min, and a PSL lifetime of <5ms that is sufficiently short for supporting rapid scanning in a two-dimensional geometry. KCl:Eu2+ was highly reusable with only a slight signal decrease of ~3% at accumulated doses over 100Gy, which could be managed by a periodic recalibration. The detected PSL signal strength of the dosimeter in the proton field had been calculated accurately to a maximum discrepancy of 2% using known physical quantities along with its prior signal strength as measured in a photon field at the same dose-to-water. This discrepancy might be attributed to an under-response due to linear energy transfer (LET) effect. However, comparisons of depth-dose measurements in a spread-out Bragg peak (SOBP) field with a parallel-plate ionization chamber showed no clear evidence of LET effects. Furthermore, range measurements agreed with ionization chamber measurements to within 1mm. KCl:Eu2+ showed linear response over a large dynamic range for proton irradiations and reliably reproduced SOBP measurements as measured by ionization chambers. Its relatively low atomic number of 18 and near LET independence make it suited for quantitative proton dosimetry. In addition, its high radiation hardness means that it can be reused numerous times. Any potential measurement artifacts encountered in complex irradiation conditions should be able to be corrected for using known physical quantities.

Evaluating inorganic compounds as air substitute materials in photon irradiation

Different inorganic materials were evaluated as substitutes for air, in photon radiation environments. The materials were evaluated based on their: total mass attenuation coefficients, mass-energy absorption coefficients, total electron mass stopping powers. Common inorganic compounds and mixtures not containing carbon were theoretically tested with the aim to find a solid or liquid air substitute material for photon radiation. As presented in this work, the best results of these tests were achieved for liquid nitric acid diluted in water at 81 wt%. This solution exhibits hitherto unknown properties similar to air for photon radiation in the energy region 0.1 to 1000 MeV and can be used for air photoactivation determination as well. The inherent property of this aqueous solution is that it allows simultaneous determination of all photonuclear reaction yields from nitrogen and oxygen in a wide range of photon energies. Additionally, this aqueous solution does not contain any other constituent elements, which could affect the accuracy of this determination.

Parametrization of multi-energy CT projection data with eigentissue decomposition

The purpose of this work is, firstly, to propose an optimized parametrization of the attenuation coefficient to describe human tissues in the context of projection-based material characterization with multi-energy CT. The approach is based on eigentissue decomposition (ETD). Secondly, to evaluate its benefits in terms of accuracy and precision of radiotherapy-related parameters against established parametrizations. The attenuation coefficient is parametrized as a linear combination of virtual materials, eigentissues, obtained by performing principal component analysis on a set of reference tissues in order to optimally represent human tissue composition. Two implementations of ETD are compared with other pre-reconstruction formalisms established for dual-energy and photon-counting CT in a simulation framework. The first implementation uses a single set of eigentissues to describe all human tissues, while the second uses different sets of eigentissues to characterize soft tissues and bones, and includes a post-reconstruction classification step. The simulation framework evaluates the reconstruction accuracy of various radiotherapy-related quantities over a range of 71 human tissues for various noise levels. Compared to conventional parametrizations, the first implementation of ETD reduces the mean error and root-mean-square error (RMSE) in two radiotherapy-related quantities (the proton stopping power and the mass energy absorption coefficient of 21 keV photons from 103Pd seeds used in brachytherapy) for all noise levels and modalities investigated. This illustrates that a decomposition basis selected with principal component analysis is superior to an arbitrary pair of materials to describe human tissues. The mean error on radiotherapy-related parameters can be further reduced with the classification-based approach. In the context of pre-reconstruction material characterization with multi-energy CT, parametrizing the attenuation coefficient with eigentissues provides a more accurate and precise evaluation of human tissues properties for radiotherapy. Accurate quantification can thus be achieved without the need to parametrize tissues using unphysical parameters, such as the energy-dependent effective atomic number.

Synthetic polymer hydrogels as potential tissue phantoms in radiation therapy and dosimetry

The efficacy of synthetic polymers as hydrogel phantoms for radiation therapy and dosimetry has been investigated for photon and charged particle (electron, proton and alpha particle) interactions. Tissue equivalence has been studied in terms of photon mass energy-absorption coefficients, KERMA (kinetic energy released per unit mass), equivalent atomic number and energy absorption build-up factors, relative to human tissues (skin, soft tissue, cortical bone and skeletal muscle), in the energy range 0.015–15 MeV. For charged particle interactions, ratio of effective atomic number is examined for tissue-equivalence in the energy region of 10 keV–1 GeV. Well established theoretical formulations are used for computation of photon mass-energy absorption effective atomic number, electron density and KERMA. Five-parameter geometric progression (G-P) fitting approximation is used to compute the values of energy absorption build-up factors. Effective atomic number for charged particle interaction is determined using logarithmic interpolation method. Using the analytical methodology, it has been revealed that all the selected synthetic polymers have good tissue-equivalence relative to all tissue except cortical bone. In particular, polyglycolic acid (PGA) and poly-lactic-co-glycolic acid (PLGA) prove to be best substitute material for photon interactions. On the other hand, % difference between effective atomic number for charged particle relative to human tissues is found least for polyethylene glycol (PEG) demonstrating adequate tissue-equivalence. Therefore, the present study is expected to be useful to choose most appropriate phantom material for radiation therapy.

On the relativistic impulse approximation for the calculation of Compton scattering cross sections and photon interaction coefficients used in kV dosimetry

We calculate differential and integrated cross sections for the Compton interaction as well as mass attenuation (), mass energy-transfer (), and mass energy-absorption () coefficients, within the relativistic impulse approximation (RIA) using Compton profiles (CPs) obtained from unrestricted Hartree–Fock electron densities. We investigate the impact of using molecular as opposed to atomic CPs on dosimetric photon interaction coefficients for air, water and graphite, and compare our cross sections to the simpler Waller–Hartree (WH) and Klein–Nishina (KN) formalisms. We find that differences in and resulting from the choice of CPs within the RIA are small relative to the differences between the RIA, WH, and KN calculations. Surprisingly, although the WH binding corrections seem accurate when considering , there are significant discrepancies between the WH and RIA results when we look at . The WH theory can differ substantially from the predictions of KN and the RIA in the tens of keV range (e.g. 6%–10% at 20 keV), when Compton scattering becomes the dominant interaction mechanism. For lower energies, the disagreement further grows to about one order of magnitude at 1 keV. However, since the photoelectric effect transfers more energy than the Compton interaction in the tens of keV range and below, the differences in the total values resulting from the choice of Compton models (KN, WH, or RIA) are not larger than 0.4%, and the differences between WH and the other two theories are no longer prominent.

Absorbed dose to water determination for kilo-voltage X-rays using alanine/EPR dosimetry systems

Alanine's relative response to kilo-voltage X-rays, compared to 60Co reference quality beam, was studied in this work, in order to determine correction factors to be applied to alanine's response when irradiated with low to medium energy X-rays (up to 300 keV).The relative response to kilo-voltage X-rays of Aerial's alanine dosimeters was determined by three distinct methods: experimental measurements using alanine dosimeters and a calibrated PTW Farmer 30013 ion chamber, Monte Carlo simulations using MCNPX code and finally, analytical calculations based on weighting of X-ray spectra by NIST's published mass energy absorption coefficients. Two sets of X-ray beam qualities, covering high voltages ranging from 50 kV up to 280 kV, were used to study the energy dependence of the alanine dosimeter's response. Obtained results were consistent within 2.1% (average standard deviation at k = 1).

Target biological tissue and energy influence on dose enhancement factor produced by gold nanoparticles and its relevant radiological properties

Understanding the radiation dose enhancement factor (DEF) influencing parameter and relevant radiological properties is important for the accurate estimation of absorbed dose in nanoparticle enhanced X-ray therapy (NEXT). In this present study, target tumor tissue influence on DEF produced by 18 mg/g gold nanoparticle (GNP) in ten various biological samples and relevant radiological properties were studied over 15KeV-15MeV energies. The DEF was calculated with the help of mass energy-absorption coefficients (μen/ρ) values. Mass attenuation coefficient (μ/ρ), (μen/ρ), photoelectric absorption coefficients were computed with the help of the XCOM program. Energy absorption buildup factor (EABF), exposure buildup factor (EBF) and effective atomic number (Zeff) were calculated by EXABCAL and auto Zeff computer program respectively. DEF were significantly varied according to target biological tissue elemental composition and incident photon energies. Among the ten various biological samples, adipose tissue target produces higher DEF which have the lower Zeff and bone produce lower DEF which possess higher Zeff. Optimal energy for the maximum DEF is 40 KeV and 100 KeV for soft tissues and bone respectively. EABF and EBF of GNP doped tissues were discussed as the function of energy and elemental composition and mean free path up 40 mfp. Energy and inhomogeneity correction factors are necessary for the accurate estimation of DEF. These results are helpful for developing the treatment planning algorithms and dosimetry for NEXT. Age and calcification dependent variation of the elemental composition of the target tissue and its effect on DEF need to account for the future work.

Study of radiation interaction parameters for organic compounds at gamma photon energies different from available standard radioisotopes

The present work emphasizes on the transmission of gamma photons, having energies in the range (241.8–401.8 keV) obtained by Compton scattering technique, to determine mass-attenuation coefficients (μm), molar-extinction coefficients (ε), mass-energy absorption coefficient (μen/ρ), effective atomic number (Zeff), mean free path (MFP), half value layer (HVL), total atomic (σt.a) and electronic (σt.el) cross-sections, and Hounsfield number (H) of various organic compounds like Alcohols, Aldehydes, Ketones, Esters, Amines, Benzene compounds and Water, and further used as radiation shielding. The WinXcom software package is used to compare the experimentally deduced radiation interaction parameters with theory. The theoretical and experimental results are in good agreement within permissible experimental uncertainty. The radiation shielding parameters have been found to vary with gamma-ray energy and effective atomic number for these organic compounds under present investigations.

Feasibility study of using polyacrylamide gel dosimeter as brain equivalent material in therapeutic energy range of X-rays

In this paper the feasibility study of using polyacrylamide gels as a brain equivalent material has been performed. Thus, the parameters of mass energy absorption coefficient (μen/ρ), mass stopping power (S/ρ), effective atomic number (Zeff), mass attenuation coefficient (μeff/ρ) and absorbed dose delivered to polyacrylamide gel (D) were determined for this gel using analytical and Monte Carlo methods and were compared with brain reference material. The calculation results reveal that the relative difference between the calculated μen/ρ, S/ρ, Zeff, μeff/ρ and D for polyacrylamide gel and those for brain are 1.32%, less than 1%, less than 2%, less than 4% and less than 1%, respectively in therapeutic energy range. Consequently, like water, polyacrylamide gel can be also used for designing and construction of head and neck phantoms applied for validation of medical algorithms used in treatment planning systems. The advantage of using polyacrylamide gel as a brain equivalent material in comparison to water is that this gel is a reliable X and gamma rays dosimeter applicable for three dimensional dose distribution determination. Also, other advantages of this gel are its low price, availability and forming it in different sizes and shapes. These properties of the polyacrylamide gel make it beneficial as brain equivalent material in designing and construction of head and neck phantoms.