Artículos
desde 2016...
2018
Water-equivalence of gel dosimeters for radiology medical imaging
M. Valente, J. Vedelago, D. Chacón, F. Mattea, J. Velásquez, P. Pérez. Applied Radiation and Isotopes, In Press, March 2018.
International dosimetry protocols are based on determinations of absorbed dose to water. Ideally, the phantom material should be water equivalent; that is, it should have the same absorption and scatter properties as water. This study presents theoretical, experimental and Monte Carlo modeling of water-equivalence of Fricke and polymer (NIPAM, PAGAT and itaconic acid ITABIS) gel dosimeters. Mass and electronic densities along with effective atomic number were calculated by means of theoretical approaches. Samples were scanned by standard computed tomography. Photon mass attenuation coefficients and electron stopping powers were examined. Theoretical, Monte Carlo and experimental results confirmed good water-equivalence for all gel dosimeters. Overall variations with respect to water in the low energy radiology range (up to 130kVp) were found to be less than 3% in average.
2017
Optimization of the sensitivity/doses relationship for a bench-top EDXRF system used for in vivo quantification of gold nanoparticles
M. Santibáñez, R. Saavedra, M. Vásquez, F. Malano, P. Pérez, M. Valente, R.G.Figueroa. Applied Radiation and Isotopes, Volume 129, Pages 19-27; November 2017.
The present work is devoted to optimizing the sensitivity-doses relationship of a bench-top EDXRF system, with the aim of achieving a detection limit of 0.010 mg/ml of gold nanoparticles in tumor tissue (clinical values expected), for doses below 10 mGy (value fixed for in vivo application). Tumor phantoms of 0.3 cm3 made of a suspension of gold nanoparticles (15 nm AurovistTM, Nanoprobes Inc.) were studied at depths of 0–4 mm in a tissue equivalent cylindrical phantom. The optimization process was implemented configuring several tube voltages and aluminum filters, to obtain non-symmetrical narrow spectra with fixed FWHM of 5 keV and centered among the 11.2–20.3 keV. The used statistical figure of merit was the obtained sensitivity (with each spectrum at each depth) weighted by the delivered surface doses. The detection limit of the system was determined measuring several gold nanoparticles concentrations ranging from 0.0010 to 5.0 mg/ml and a blank sample into tumor phantoms, considering a statistical fluctuation within 95% of confidence. The results show the possibility of obtaining a detection limit for gold nanoparticles concentrations around 0.010 mg/ml for surface tumor phantoms requiring doses around 2 mGy.
2016
Development and characterization of a microCT facility
M. Valente, D. Graña, F. Malano, P. Pérez, C. Quintana, G. Tirao, J. Vedelago. IEEE Latin America Transactions, Volume 14, Issue 9, Pages 3967-3973; September 2016.
This work reports the design, construction, characterization and application of a novel X-ray imaging beamline at Laboratorio de Investigación e Instrumentación en Física Aplicada a la Medicina e Imágenes por Rayos X - LIIFAMIRx - University of Cordoba and Institute of Physics E. Gaviola - CONICET, Argentina. This development is the first phase in the construction of the integral facility for combining different imaging modalities, like absorption contrast images by primary and scattering contributions, high-resolution micro-tomography, elastic scattering and X-ray fluorescence scanning for chemical composition and surface characterizations. The progress and results here reported concern mainly to the micro-tomography beam-line. This technique is already operative and it was used for several academic researches, application studies and services. The obtained results for the characterization of organic and inorganic samples demonstrated the feasibility and reliability of the developed facility. Accordingly, this work reports specific characteristics about its design, construction, and operation supporting its employment in a wide range of especial applications that might not be accomplished by other available techniques. Moreover, some application studies, mainly focused on biological samples, are presented.
Beta-minus emitters Dose Point Kernel estimation model comprising different tissues for nuclear medicine dosimetry applications
P. Pérez, F. Geser, I. Scarinci, F. Malano, M. Valente. International Journal of Nuclear Medicine Research, Volume 3, Issue 2, Pages 45-55; September 2016.
The use of β-emitters for therapy purposes is one of the most extended procedures for tumor treatments in nuclear medicine practices over the last years. The constantly increasing dose delivery to healthy tissues in this practices, due to their high linear energy transfer and their radiobiological characteristics, might lead to complications in radiosensitive organs/tissues. Research efforts should be conducted to the development of tools and methods devoted to perform precise dosimetric calculations to deal with this issue and assess accurately dosimetric estimations on patients treated regions.
When performing dosimetry at organ level it is usual to assume some approximations on calculations, like uniformity in activity distribution within source regions, homogeneous media distribution for patient treated regions and uniform delivered dose on target organs. In this work, a formula to obtain Dose Point Kernel for different biological media is presented. Results are collated with Monte Carlo simulations suggesting a behavior that can be splitted in three groups, in accordance to their differences against the stochastic estimations: a) skin, blood and brain present differences within the 5% in comparison with the reference data; b) skeletal muscle, soft tissue, striated muscle and adipose tissue have differences lower than 20%; and c) compact bone, cortical bone and lung tissue differences are found above 50%.
This introduction of a medium-specific Dose Point Kernel calculation method could potentially lead to future improvements on dosimetric systems, limiting for now this model to tissues with effective atomic number closed to liquid water.
Fricke gel dosimeter with improved sensitivity for low-dose-level measurements
M. Valente, W. Molina, L. Carrizales Silva, R. Figueroa, F. Malano, P. Pérez, M. Santibañez, J. Vedelago. Journal of Applied Clinical Medical Physics, Volume 17, Issue 4, Pages 402-417; July 2016.
Fricke solution has a wide range of applications as radiation detector and dosimetry. It is particularly appreciated in terms of relevant comparative advantages, like tissue-equivalence when prepared in aqueous media like gel matrix, continuous mapping capability, independence of dose rate and incident direction, as well as linear dose response. This work presents the development and characterization of an improved Fricke gel system, based on modified chemical compositions, making possible its application in clinical radiology due to its improved sensitivity. Properties of standard Fricke gel dosimeter for high-dose levels are used as a starting point, and suitable chemical modifications are introduced and carefully investigated in order to attain high resolution for low-dose ranges, like those corresponding to radiology interventions. The developed Fricke gel radiation dosimeter system achieves the expected typical dose-dependency, showing linear response in the dose range from 20 up to 4000 mGy. Systematic investigations including several chemical compositions are carried out in order to obtain an adequate dosimeter response for low-dose levels. A suitable composition from among those studied is selected as a good candidate for low-dose-level radiation dosimetry consisting of a modified Fricke solution fixed to a gel matrix containing benzoic acid along with sulfuric acid, ferrous sulfate, Xylenol orange, and tridistilled water. Dosimeter samples are prepared in standard vials for in-phantom irradiation and further characterization by spectrophotometry measuring visible light transmission and absorbance before and after irradiation. Samples are irradiated using typical X-ray tubes for radiology and calibrated Farmer-type ionization chamber is used as reference to measure dose rates inside phantoms at vial locations. Once sensitive material composition is optimized, dose-response curves show significant improvement regarding overall sensitivity for low dose levels. The aim of this work consists of implementing the optimized gel dosimeter to perform direct measurements of absorbed dose in samples irradiated during microcomputed tomography scanning in order to preliminary assess dose levels for further scanning of small animals for further applications in veterinary and paleontology. As a first attempt, dose distributions were measured in water-equivalent phantoms having dimensions comparable to small animals, 100 to 1000 cm3, approximately. According to the obtained results, it is found that the proposed method shows satisfactory reliability and adequate performance for a promising gel dosimetry system.
Non-destructive structural assay using x-ray micro-tomography to estimate mass density differences in rabbit bone samples
International Journal of Morphology, Volume 34, Issue 4, Pages 1232-1238; 2016.
When performing studies on bone samples aiming at analyzing its physical characteristics such as hardness, density and health, typically it is used to utilize different equipment for the quantification of electron density, which results proportional to mass density, which is directly related to bone mineral density. The test known as bone densitometry is usually done using X-ray equipment, ultrasound or through the utilization of radioactive isotopes. This analysis quantifies the amount of mineral bone on a surface and is usually implemented to assess, among others, risks of fractures or the osteoporosis state in a patient. The computed tomography technique uses two-dimensional X-ray images and tomographic reconstruction methods implemented on computational algorithms to obtain information about the internal structure of an object in a nondestructively way. Specially developed equipment able to obtain images with sub-millimeter resolution, results in the technique known as micro-tomography. The ability to study bone structures at sub-millimeter levels and obtain three-dimensional morphological images with electron density information, presents an important option for specific studies on bone growth and studies on new components that allow the growth of damaged tissues. In this paper rabbits cranium bone samples where certain areas have been damaged and have been filled with different substances specially designed to evaluate repair responses on bone tissue are analyzed. The analysis is performed in order to study the performance of the micro-tomography technique developed in the laboratory in order to observe its potentiality in this type of studies and the ability of these analysis in the characterization of the physical properties of such samples.