Search for Tissue Equivalent Materials Based on Exposure and Energy Absorption Buildup Factor Computations

Tissue equivalent materials (TEM) are frequently used in research as a means to determine the delivered dose to patients undergoing various therapeutic procedures. They are used in routine quality assurance and quality control procedures in diagnostic and therapeutic physics. However, very few materials that are tissue equivalent have been developed for use in research at the low photon energies involved in diagnosis radiology. The objective of this study is to describe a series of TEMs designed to radiographically imitate human tissue at diagnostic photon energies. TEMs for adipose, cortical bone, fat, lung, and muscle tissues were investigated in terms of energy absorption and exposure buildup factors for photon energy range 15–150 keV and for penetration depths up to 40 mean free path. BUF was computed based on GP-fitting method. Moreover, we also compared some radiological properties, including the total attenuation and the energy-absorption attenuation, the effective atomic number, and the CT number at 30, 100, and 120 kVp. We found that SB3, Glycerol trioleate, and MS15 perfectly mimic cortical bone, fat, and muscle tissues, respectively. Additionally, AP6 and Stracey latex are good TEM for adipose and lung tissues, respectively. The results of this work should be useful in radiation diagnosis and dosimetry applications for the large physician researcher community.

High-sensitive colour indicator of absorbed dose of epithermal neutrons radiation

In our study, the high-sensitivity colour indicator of the absorbed dose of radiation of epithermal neutrons with energy 0 to 10 keV for dosimetry of low-energy neutrons was developed. We had been developed an indicator on the basis of the dye solution of arsenazo III and gadopentetic acid, allowing precisely define of absorbed dose in the range 2 to 103 Gy. The properties of arsenazo III as metallic indicator, which changes colour after binding of free ions of metals, were used. Colour of the indicator solution before irradiation and after it is stable enough in time at storage in the dark, at artificial illumination or at scattered sunlight. The developed indicator, consisting of a solution of arsenazo III and gadopentetic acid, allows estimating the absorbed dose of epithermal neutron irradiation with good accuracy and reduces the error of measurement related to changing colour of dye under the influence of other factors (light, temperature etc.) Dosimeter is tissue-equivalent and possesses a high-sensitivity neutron radiation due to the content of gadolinium in solution, which has great neutron capture cross-section. The developed dosimeter persists spectrophotometric characteristics after irradiaion within few weeks that allows to use it for measurement of the absorbed dose, both in real time mode and with the delayed measurement within few weeks.

A Monte Carlo investigation of some important radiation parameters and tissue equivalency for photons below 1 keV in human tissues

The attenuation coefficients are important input values in estimating not only the dose and exposure in radiotherapy and medical imaging, but also in the proper design of photon shields. While studies are widely available above 1 keV, the attenuation coefficients of human tissues for photon energies less than 1 keV have not been studied yet. In this study, the attenuation coefficients of water and some human tissues were estimated for low energy photons using the MCNP6.1 code in the energy region 0.1 keV-1 keV. Mass attenuation coefficients were estimated at photon energies of 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950 and 1000 eV for water and ten human tissues (Soft, Breast, Lung, Bone, Brain, Eye lens, Ovary, Skin, Thyroid and Prostate). Results were compared with those available in literature and a fairly good agreement has been obtained. These data were then used to calculate the mean free path, half value layer, tenth value layer, effective atomic number and specific gamma-ray constant (useful for calculation of dose rate) as well. Moreover, for comparison the effective atomic number of the water has been obtained using the results of this work and using the data available in NIST database from 0.1 to 1 keV. In addition, the human tissues were compared with some tissue equivalent materials in terms of effective atomic number and specific gamma-ray constant to study the tissue equivalency from the results, the muscle-equivalent liquid with sucrose has been found to be the best tissue equivalent material for soft tissue, eye lens and brain with relative difference below 4.1%.

The Effect of Ionising Radiation on the Luminescence Properties of Fluoroperovskites

<p>The luminescence of crystalline compounds can be used to monitor many physical phenomena, including doses of ionising radiation. Optically stimulated luminescence (OSL), thermoluminescence (TL), and radiophotoluminescence (RPL) have been successfully employed in dosimetry. However, few materials possess both the structural and luminescence properties required for medical dosimetry. This thesis aimed to investigate the luminescence features of the class of compounds known as fluoroperovskites. Emphasis was placed on studying the effects of irradiation on the luminescence properties, such that the compounds could be evaluated regarding potential applications in clinical dosimetry. Samples were primarily characterised using photoluminescence (PL), radioluminescence (RL), OSL, RPL, TL, and transmittance spectroscopy. OSL was observed in the majority of samples due to the existence of electron trapping F-type centres. F-centre/Mn complexes were observed in all AMgF3:Mn compounds after irradiation and the energy levels of the complexes in each compound were experimentally determined. The most promising potential dosimeter host material was the near tissue-equivalent NaMgF3. When doped with Mn2+, the compound exhibited RPL via the formation of F-centre/Mn complexes and OSL via several trapping centres. The RPL could be probed independently to the OSL such that the compound could function as a hybrid OSL/RPL dosimeter. In the NaMgF3:Ln compounds, RPL occurred via the radiation-induced reduction Ln3+ → Ln2+ for Ln = Sm, Dy, and Yb. The reduction Sm3+ → Sm2+ was highly stable and could be non-destructively probed independently to the OSL. The Sm doped compound also exhibited radiation-induced conductivity that could be coupled with the RL, such that the compound could function as a real-time hybrid optical/electrical dosimeter. Charge kinetics, thermal quenching, and binding energy models were developed and applied to the compounds. Finally, a two-dimensional readout system was designed and constructed. The capabilities of the system were evaluated using the OSL of NaMgF3:Eu and NaMgF3:Mn. Sensitivities to doses from < 10 mGy to > 1 Gy were obtained along with sub-millimetre spatial resolutions.</p>

The Effect of Ionising Radiation on the Luminescence Properties of Fluoroperovskites

<p>The luminescence of crystalline compounds can be used to monitor many physical phenomena, including doses of ionising radiation. Optically stimulated luminescence (OSL), thermoluminescence (TL), and radiophotoluminescence (RPL) have been successfully employed in dosimetry. However, few materials possess both the structural and luminescence properties required for medical dosimetry. This thesis aimed to investigate the luminescence features of the class of compounds known as fluoroperovskites. Emphasis was placed on studying the effects of irradiation on the luminescence properties, such that the compounds could be evaluated regarding potential applications in clinical dosimetry. Samples were primarily characterised using photoluminescence (PL), radioluminescence (RL), OSL, RPL, TL, and transmittance spectroscopy. OSL was observed in the majority of samples due to the existence of electron trapping F-type centres. F-centre/Mn complexes were observed in all AMgF3:Mn compounds after irradiation and the energy levels of the complexes in each compound were experimentally determined. The most promising potential dosimeter host material was the near tissue-equivalent NaMgF3. When doped with Mn2+, the compound exhibited RPL via the formation of F-centre/Mn complexes and OSL via several trapping centres. The RPL could be probed independently to the OSL such that the compound could function as a hybrid OSL/RPL dosimeter. In the NaMgF3:Ln compounds, RPL occurred via the radiation-induced reduction Ln3+ → Ln2+ for Ln = Sm, Dy, and Yb. The reduction Sm3+ → Sm2+ was highly stable and could be non-destructively probed independently to the OSL. The Sm doped compound also exhibited radiation-induced conductivity that could be coupled with the RL, such that the compound could function as a real-time hybrid optical/electrical dosimeter. Charge kinetics, thermal quenching, and binding energy models were developed and applied to the compounds. Finally, a two-dimensional readout system was designed and constructed. The capabilities of the system were evaluated using the OSL of NaMgF3:Eu and NaMgF3:Mn. Sensitivities to doses from < 10 mGy to > 1 Gy were obtained along with sub-millimetre spatial resolutions.</p>

A Study on the Performance of a Silicon Photodiode Sensor for a Particle Dosimeter and Spectrometer

A lunar vehicle radiation dosimeter (LVRAD) has been proposed for studying the radiation environment on the lunar surface and evaluating its impact on human health. The LVRAD payload comprises four systems: a particle dosimeter and spectrometer (PDS), a tissue-equivalent dosimeter, a fast neutron spectrometer, and an epithermal neutron spectrometer. A silicon photodiode sensor with compact readout electronics was proposed for the PDS. The PDS system aims to measure protons with 10–100 MeV of energy and assess dose in the lunar space environment. The manufactured silicon photodiode sensor has an effective area of 20 mm × 20 mm and thickness of 650 μm; the electronics consist of an amplifier, analog pulse processor, and a 12-bit analog-to-digital converter for signal readout. We studied the responses of silicon sensors which were manufactured with self-made electronics to gamma rays with a wide range of energies and proton beams.

Cell-assembled extracellular matrix (CAM): a human biopaper for the biofabrication of pre-vascularized tissues able to connect to the host circulation in vivo

When considering regenerative approaches, the efficient creation of a functional vasculature, that can support the metabolic needs of bioengineered tissues, is essential for their survival after implantation. However, it is widely recognized that the post-implantation microenvironment of the engineered tissues is often hypoxic due to insufficient vascularization, resulting in ischemia injury and necrosis. This is one of the main limitations of current tissue engineering applications aiming at replacing significant tissue volumes. Here, we have explored the use of a new biomaterial, the cell-assembled extracellular matrix (CAM), as a biopaper to biofabricate a vascular system. CAM sheets are a unique, fully biological and fully human material that has already shown stable long-term implantation in humans. We demonstrated, for the first time, the use of this unprocessed human ECM as a microperforated biopaper. Using microvalve dispensing bioprinting, concentrated human endothelial cells (30 millions ml−1) were deposited in a controlled geometry in CAM sheets and cocultured with HSFs. Following multilayer assembly, thick ECM-based constructs fused and supported the survival and maturation of capillary-like structures for up to 26 d of culture. Following 3 weeks of subcutaneous implantation in a mice model, constructs showed limited degradative response and the pre-formed vasculature successfully connected with the host circulatory system to establish active perfusion.This mechanically resilient tissue equivalent has great potential for the creation of more complex implantable tissues, where rapid anastomosis is sine qua non for cell survival and efficient tissue integration.

Induction of Apoptotic Temperature in Photothermal Therapy under Various Heating Conditions in Multi-Layered Skin Structure

Recently, photothermal therapy has attracted attention as an alternative treatment to conventional surgical techniques because it does not lead to bleeding and patients quickly recover after treatment compared to incisional surgery. Photothermal therapy induces tumor cell death through an increase in the temperature using the photothermal effect, which converts light energy into thermal energy. This study was conducted to perform numerical analysis based on heat transfer to induce apoptosis of tumor tissue under various heating conditions in photothermal therapy. The Monte Carlo method was applied to evaluate a multi-layered skin structure containing squamous cell carcinoma. Tissue-equivalent phantom experiments verified the numerical model. Based on the effective apoptosis retention ratio, the numerical analysis results showed the quantitative correlation for the laser intensity, volume fraction of gold nanorods injected into the tumor, and cooling time. This study reveals optimal conditions for maximizing apoptosis within tumor tissue while minimizing thermal damage to surrounding tissues under various heating conditions. This approach may be useful as a standard treatment when performing photothermal therapy.