Use of Gaussian-type functions for flux-based dose calculations in carbon ion therapy.

In radiation therapy, it is very important to ensure that the radiation dose is correctly delivered to the patient. This is achieved by obtaining quantitative dose measurements for beam calibration in the treatment planning system. Dose calculations should be performed with the required accuracy to a degree of uncertainty of less than 1%. The measurement of the absorbed dose in and around body tissues irradiated with carbon ions requires careful use of materials selected from established phantom and radiation detectors. The main advantage of such materials is that when information on the energy and nature of charged particles at the desired point is incomplete or inaccurate, they can allow determination of the absorbed dose. In general, radiation interactions in a tissue representation caused by carbon ions can be characterized by calculating the linear stopping power. Carbon ions have a limited penetration depth within human tissues that depends on the energy and stopping power of these ions as they penetrate into the body. The purpose of the present study was to calculate the stopping power, range and dose to intestinal and prostate tissues of carbon ions. The stopping power values of these tissues were specified by the effective charge approach method. The 5ZaPa-NR-CV, pcemd-4 and pcSseg-4 sets of Gaussian-type functions were employed for the calculation of electronic charge density. Range calculations were made by means of the Gaussian quadrature method, making use of the continuous slowing down approximation. Flux-based dose calculations were also carried out in accordance with the Bragg-Gray theorem using the Geant4 and FLUKA simulation toolkits. The results were compared with each other and with the SRIM and CasP datasets. Then, depth-dose distributions and range values were verified by positron emission activity using the GATE toolkit. Among the different types of Gaussian functions used here, the best semi-analytical result was found for the 5ZaPa-NR-CV set. The results obtained in the present study can be used for dose verification and dose reconstruction in charged particle radiotherapy and for radiation research on the interaction of radiation with matter. The results calculated here will be useful for quantifying uncertainties associated with stopping power, range, and reconstruction of dose in charged particle therapy.

Surface characterization and antibacterial efficiency of well-ordered TiO2 nanotube surfaces fabricated on titanium foams.

Titanium (Ti)-based implants are not compatible enough due to their bio-inert character, insufficient antibacterial capabilities and stress-shielding problem for dental and orthopaedic implant applications. Thus, this work focused to fabricate, analyze and improve antibacterial properties titanium dioxide (TiO2) nanotube array surfaces on Ti foam by anodic oxidation (AO) process. The well-ordered nanotube arrays with approximately 75 nm were successfully fabricated at 40 V for 1 h on Ti foams. Ti and O were observed as major elements on AO-coated Ti foam surfaces. In addition, the existence of TiO2 structure was proved on AO-coated foam Ti surfaces. For potential dental and orthopedic implant application, in vitro antibacterial properties were investigated versus Staphylococcus aureus and Escherichia coli. For both bacteria, antibacterial properties of TiO2 nanotube surface were greater than bare Ti foam. The bacterial inhibition versus Staphylococcus aureus and Escherichia coli of TiO2 nanotube surfaces are improved as 53.3% and 69.4% compared to bare Ti foam.

Characterization and investigation of biological properties of silver nanoparticle-doped hydroxyapatite-based surfaces on zirconium.

The infections leading to failed implants can be controlled mainly by metal and metal oxide-based nanoparticles. In this work, the randomly distributed AgNPs-doped onto hydroxyapatite-based surfaces were produced on zirconium by micro arc oxidation (MAO) and electrochemical deposition processes. The surfaces were characterized by XRD, SEM, EDX mapping and EDX area and contact angle goniometer. AgNPs-doped MAO surfaces, which is beneficial for bone tissue growth exhibited hydrophilic behaviors. The bioactivity of the AgNPs-doped MAO surfaces is improved compared to bare Zr substrate under SBF conditions. Importantly, the AgNPs-doped MAO surfaces exhibited antimicrobial activity for E. coli and S. aureus compared to control samples.

Surface characterization, electrochemical properties and in vitro biological properties of Zn-deposited TiO2 nanotube surfaces.

In this work, to improve antibacterial, biocompatible and bioactive properties of commercial pure titanium (cp-Ti) for implant applications, the Zn-deposited nanotube surfaces were fabricated on cp-Ti by using combined anodic oxidation (AO) and physical vapor deposition (PVD-TE) methods. Homogenous elemental distributions were observed through all surfaces. Moreover, Zn-deposited surfaces exhibited hydrophobic character while bare Ti surfaces were hydrophilic. Due to the biodegradable behavior of Zn on the nanotube surface, Zn-deposited nanotube surfaces showed higher corrosion current density than bare cp-Ti surface in SBF conditions as expected. In vitro biological properties such as cell viability, ALP activity, protein adsorption, hemolytic activity and antibacterial activity for Gram-positive and Gram-negative bacteria of all surfaces were investigated in detail. Cell viability, ALP activity and antibacterial properties of Zn-deposited nanotube surfaces were significantly improved with respect to bare cp-Ti. Moreover, hemolytic activity and protein adsorption of Zn-deposited nanotube surfaces were decreased. According to these results; a bioactive, biocompatible and antibacterial Zn-deposited nanotube surfaces produced on cp-Ti by using combined AO and PVD techniques can have potential for orthopedic and dental implant applications.

Continuous slowing-down approximation ranges of biological materials for 0.05-10 MeV alpha particles by using different approach methods.

The goal of this study was to calculate the range values of alpha particles in bone, MS20 tissue substitute, and muscle targets using different approach methods. The range values were calculated using Gauss quadrature, Simpson 1/3, and trapezoidal numerical integration methods in continuous slowing-down approximation (CSDA). Overall, the Gauss quadrature method gave the best CSDA range values for the target materials. These results will be conducive to studies involving the interaction of radiation with biological materials.

In vitro biological and antimicrobial properties of chitosan-based bioceramic coatings on zirconium.

Ca-based porous and rough bioceramic surfaces were coated onto zirconium by micro-arc oxidation (MAO). Subsequently, the MAO-coated zirconium surfaces were covered with an antimicrobial chitosan layer via the dip coating method to develop an antimicrobial, bioactive, and biocompatible composite biopolymer and bioceramic layer for implant applications. Cubic ZrO2, metastable Ca0.15Zr0.85O1.85, and Ca3(PO4)2 were detected on the MAO surface by powder-XRD. The existence of chitosan on the MAO-coated Zr surfaces was verified by FTIR. The micropores and thermal cracks on the bioceramic MAO surface were sealed using a chitosan coating, where the MAO surface was porous and rough. All elements such as Zr, O, Ca, P, and C were homogenously distributed across both surfaces. Moreover, both surfaces indicated hydrophobic properties. However, the contact angle of the MAO surface was lower than that of the chitosan-based MAO surface. In vitro bioactivity on both surfaces was investigated via XRD, SEM, and EDX analyses post-immersion in simulated body fluid (SBF) for 14 days. In vitro bioactivity was significantly enhanced on the chitosan-based MAO surface with respect to the MAO surface. In vitro microbial adhesions on the chitosan-based MAO surfaces were lower than the MAO surfaces for Staphylococcus aureus and Escherichia coli.

The calculation of stopping power and range for radium, thorium and uranium using new electronic potential energy function.

In this paper, the electronic stopping power and range calculations of radium-226, thorium-229 and uranium-236 isotopes, which are natural alpha emitters, were performed for the alpha particles in the 200 keV-10 MeV energy range. The effective charge approach based on the Bethe-Bloch theory for the stopping power, the continuous slowing down approach and the Simpson 1/3 method were used for calculation of the range. To this end, new electronic potential energy functions were primarily obtained by using the Lie group method for the target elements. For electronic charge density, relativistic atomic natural orbitals based on Gaussian type orbitals were selected. The results were compared with the existing data sets in the literature. The potential energy curves obtained were irregular at certain distances, but were quite close to that of the multi-atomic target systems. The stripping distances of the target atoms and the corresponding potential energy values were determined from the potential energy functions. It was observed that the stopping power and range values were generally compatible with the SRIM and ICRU 49 data at specific error rates. By adding some correction factors to the calculations, it is predicted that the discrepancies and the error rates may be reduced. The results acquired with this innovative work can be used in the interaction of charged particles with matter, applications related to alpha decay and shielding.

[The contribution of locked screw-plate fixation with varying angle configurations to stability of osteoporotic fractures: an experimental study]. / Osteoporotik kemikte kilitli plak ve açili vida kullaniminin stabilizasyonun dayanikliligina katkisi: Deneysel çalisma.

OBJECTIVES: This experimental study was designed to find new ways of improving stabilization of fractures in osteoporotic elderly patients through alterations made in the configuration and geometry of locked screw-plate fixation used in the conventional plate technique. METHODS: Four screw configurations with varying angulations were used for plate-bone construction. Forty iron plates of high quality (100x35x3 mm) were divided into four groups and two screw holes, 3 mm in diameter, were drilled on each plate at a distance of 15 mm. In group A, the holes were drilled so that the screws would be vertically sent to the bone interface. In the remaining groups, the holes were drilled for convergent (group B, 15 degrees ) and divergent (group C, 15 degrees ; group D, 30 degrees ) screw orientation. Screw-plate fixation was tested in a modified osteoporotic bone (Osteoporotic Generic Bone, Synbone) on an Instron materials testing system with an axial pullout force of 0.1 mm/sec. Failure loads were read from load-displacement curves and the type of failure was noted. RESULTS: Screws placed in divergent orientations showed the highest axial pull-out strength (group C, 83.3 N/mm; group D, 80.8 N/mm), followed by convergent placement (72 N/mm) and vertical placement (66.7 N/mm). The type of failure was breakage of the bone sample in divergent configurations, and screw pull-out in convergent and vertical configurations. CONCLUSION: Divergent constructs may be a promising alternative to conventional screw placement in treating osteoporotic fractures.

Bioactivity and biocompatibility of hydroxyapatite-based bioceramic coatings on zirconium by plasma electrolytic oxidation.

In the present work, hydroxyapatite (HAP)-based plasma electrolytic oxide (PEO) coatings were produced on zirconium at different current densities in a solution containing calcium acetate and ß-calcium glycerophosphate by a single step. The phase structure, surface morphology, functional groups, thickness and roughness of the coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), eddy current method and surface profilometer, respectively. The phases of cubic-zirconia, calcium zirconate and HAP were detected by XRD. The amount of HAP and calcium zirconate increased with increasing current density. The surface of the coatings was very porous and rough. Moreover, bioactivity and biocompatibility of the coatings were analyzed in vitro immersion simulated body fluid (SBF) and MTT (3-(4,5-dimethyl thiazol-2yl)-2,5-diphenyl tetrazolium bromide) assay, hemolysis assay and bacterial formation. The apatite-forming ability of the coatings was evaluated after immersion in SBF up to 28days. After immersion, the bioactivity of HAP-based coatings on zirconium was greater than the ones of uncoated zirconium and zirconium oxide-based surface. The bioactivity of PEO surface on zirconium was significantly improved under SBF conditions. The bacterial adhesion of the coatings decreased with increasing current density. The bacterial adhesion of the coating produced at 0.370A/cm2 was minimum compared to uncoated zirconium coated at 0.260 and 0.292A/cm2. The hemocompatibility of HAP-based surfaces was improved by PEO. The cell attachment and proliferation of the PEO coatings were better than the one of uncoated zirconium according to MTT assay results.