Absorbed dose evaluation of Auger electron-emitting radionuclides: impact of input decay spectra on dose point kernels and S-values

The aim of this study was to investigate the impact of decay data provided by the newly developed stochastic atomic relaxation model BrIccEmis on dose point kernels (DPKs - radial dose distribution around a unit point source) and S-values (absorbed dose per unit cumulated activity) of 14 Auger electron (AE) emitting radionuclides, namely 67Ga, 80mBr, 89Zr, 90Nb, 99mTc, 111In, 117mSn, 119Sb, 123I, 124I, 125I, 135La, 195mPt and 201Tl. Radiation spectra were based on the nuclear decay data from the medical internal radiation dose (MIRD) RADTABS program and the BrIccEmis code, assuming both an isolated-atom and condensed-phase approach. DPKs were simulated with the PENELOPE Monte Carlo (MC) code using event-by-event electron and photon transport. S-values for concentric spherical cells of various sizes were derived from these DPKS using appropriate geometric reduction factors. The number of Auger and Coster-Kronig (CK) electrons and x-ray photons released per nuclear decay (yield) from MIRD-RADTABS were consistently higher than those calculated using BrIccEmis. DPKs for the electron spectra from BrIccEmis were considerably different from MIRD-RADTABS in the first few hundred nanometres from a point source where most of the Auger electrons are stopped. S-values were, however, not significantly impacted as the differences in DPKS in the sub-micrometre dimension were quickly diminished in larger dimensions. Overestimation in the total AE energy output by MIRD-RADTABS leads to higher predicted energy deposition by AE emitting radionuclides, especially in the immediate vicinity of the decaying radionuclides. This should be taken into account when MIRD-RADTABS data are used to simulate biological damage at nanoscale dimensions.Comment: 27 pages, 4 figures, 3 table

Calculated energy loss of swift He, Li, B, and N ions in SiO2, Al2O3, and ZrO2

We have calculated the electronic stopping power and the energy-loss straggling parameter of swift He, Li, B, and N ions moving through several oxides, namely SiO2, Al2O3, and ZrO2. The evaluation of these stopping magnitudes was done in the framework of the dielectric formalism. The target properties are described by means of a combination of Mermin-type energy-loss functions that characterize the response of valence-band electrons, together with generalized oscillator strengths to take into account the ionization of inner-shell electrons. We have considered the different charge states that the projectile can have, as a result of electron capture and loss processes, during its motion through the target. The electron density for each charge state was described using the Brandt-Kitagawa statistical model and, for He and Li ions, also hydrogenic orbitals. This procedure provides a realistic representation of both the excitation properties of the target electrons and the projectile charge density, yielding stopping powers that compare reasonably well with available experimental data above a few tens of keV/amu.This work was supported by the Spanish Comisión Interministerial de Ciencia y Tecnología (BFM2003-04457-C02-01 and BFM2003-04457-C02-02). S.H.A. thanks the Fundación Cajamurcia for financial support and J.M.F.V. expresses his gratitute for a travel grant from the Universitat d’Alacant

A comprehensive Monte Carlo study of CT dose metrics proposed by the AAPM Reports 111 and 200

Purpose A Monte Carlo (MC) modeling of single axial and helical CT scan modes has been developed to compute single and accumulated dose distributions. The radiation emission characteristics of an MDCT scanner has been modeled and used to evaluate the dose deposition in infinitely long head and body PMMA phantoms. The simulated accumulated dose distributions determined the approach to equilibrium function, H(L). From these urn:x-wiley:00942405:media:mp15306:mp15306-math-0001 curves, dose-related information was calculated for different head and body clinical protocols. Methods The PENELOPE/penEasy package has been used to model the single axial and helical procedures and the radiation transport of photons and electrons in the phantoms. The bowtie filters, heel effect, focal-spot angle, and fan-beam geometry were incorporated. Head and body protocols with different pitch values were modeled for x-ray spectra corresponding to 80, 100, 120, and 140 kV. The analytical formulation for the single dose distributions and experimental measurements of single and accumulated dose distributions were employed to validate the MC results. The experimental dose distributions were measured with OSLDs and a thimble ion chamber inserted into PMMA phantoms. Also, the experimental values of the urn:x-wiley:00942405:media:mp15306:mp15306-math-0002 along the center and peripheral axes of the CTDI phantom served to calibrate the simulated single and accumulated dose distributions. Results The match of the simulated dose distributions with the reference data supports the correct modeling of the heel effect and the radiation transport in the phantom material reflected in the tails of the dose distributions. The validation of the x-ray source model was done comparing the CTDI ratios between simulated, measured and CTDosimetry data. The average difference of these ratios for head and body protocols between the simulated and measured data was in the range of 13-17% and between simulated and CTDosimetry data varied 10-13%. The distributions of simulated doses and those measured with the thimble ion chamber are compatible within 3%. In this study, it was demonstrated that the efficiencies of the urn:x-wiley:00942405:media:mp15306:mp15306-math-0003 measurements in head phantoms with nT = 20 mm and 120 kV are 80.6% and 87.8% at central and peripheral axes, respectively. In the body phantoms with urn:x-wiley:00942405:media:mp15306:mp15306-math-0004= 40 mm and 120 kV, the efficiencies are 56.5% and 86.2% at central and peripheral axes, respectively. In general terms, the clinical parameters such as pitch, beam intensity, and voltage affect the Deq values with the increase of the pitch decreasing the Deq and the beam intensity and the voltage increasing its value. The H(L) function does not change with the pitch values, but depends on the phantom axis (central or peripheral). Conclusions The computation of the pitch-equilibrium dose product, urn:x-wiley:00942405:media:mp15306:mp15306-math-0005, evidenced the limitations of the urn:x-wiley:00942405:media:mp15306:mp15306-math-0006 method to determine the dose delivered by a CT scanner. Therefore, quantities derived from the urn:x-wiley:00942405:media:mp15306:mp15306-math-0007 propagate this limitation. The developed MC model shows excellent compatibility with both measurements and literature quantities defined by AAPM Reports 111 and 200. These results demonstrate the robustness and versatility of the proposed modeling method

Tres impresos de la Biblioteca del Infantado, heredadeos pora la Casa Ducal de Osuna, que se conservan en la biblioteca de la Universidad Pontificia de Comillas

Se describen tres impresos de la biblioteca de la Casa Ducal del Infantado, que habían pasado a engrosar la Biblioteca del XI Duque de Osuna, Pedro de Alcántara Téllez-Girón y Beaufort Spontin, en 1834, al heredar el Ducado del Infantado con todas sus posesiones, muebles e inmuebles, entre las que se encontraba la Biblioteca de los Mendoza. Actualmente, se conservan en la Biblioteca de la Universidad Pontificia Comillas

Discards of Spanish Trawler Fleets Operating in the Bay of Biscay in 2000

A stratified sampling programme by gear and port was carried out by observers on board vessels in 2000 to study the discard behaviour of trawler fleets operating off Spanish North Atlantic coasts. No relationship between discards in weight or numbers and haul duration was found, so the results in weight are presented in kilograms per haul instead of kilograms per hour, as is usual for catches. The data were analysed in order to find groups of ports with a similar behaviour and to reduce the number of strata (30 as a result of the crossing of 10 main ports and 3 types of towed gears). The reduction in the number of strata (from the 30 original strata to the 9 new groups obtained) would mean a high improvement in efficiency for raising purposes, for stock assessment needs and for new Spanish sampling programmes. Significant differences in discards between groups of ports were found. Species composition of discards by stratum is given as a percentage of the total weight, based on data collected by the observers on board vessels. There are also differences in the discarded species composition for the different groups of ports obtained.Para estudiar los descartes de las flotas de arrastre que pescan en las costas Noratlánticas españolas se llevó a cabo, durante el año 2000, un programa de muestreo con observadores a bordo. El tipo de muestreo fue estratificado por arte y puerto. No se ha encontrado relación entre los descartes en peso o en número y la duración del lance, por lo tanto, los resultados se presentan en kilos por lance en lugar de kilos por hora, como es habitual para las capturas. Para reducir el número de estratos (que eran 30 como resultado de cruzar 10 puertos principales con los tres tipos de arte de arrastre considerados) se analizaron los datos en busca de los grupos de puertos con comportamiento similar. La reducción en el número de estratos (de los 30 originales a los 9 nuevos grupos obtenidos) podría aumentar la eficiencia de los muestreos especialmente con vista a la estimación de valores totales útiles en evaluación y futuros programas de muestreo. Las diferencias entre los descartes de los distintos grupos de puertos obtenidos resultaron significativas. Los resultados incluyen la composición específica del descarte por estrato, en porcentaje del peso total, basada en datos recogidos con observadores a bordo. Estos resultados también muestran diferencias entre los diferentes grupos de puertos.Publicado

La reconstrucción de la Biblioteca de la Casa Ducal de Osuna: Proyecto del Grupo de Trabajo de Patrimonio Bibliográfico de la Red de Bibliotecas Universitarias Españolas (REBIUN)

Fac. de Ciencias de la DocumentaciónFac. de Ciencias de la InformaciónTRUEpu

Monte Carlo dosimetry for forthcoming clinical trials in x-ray microbeam radiation therapy

The purpose of this work is to define safe irradiation protocols in microbeam radiation therapy. The intense synchrotron-generated x-ray beam used for the treatment is collimated and delivered in an array of 50 μm-sized rectangular fields with a centre-to-centre distance between microplanes of 400 μm. The absorbed doses received by the tumour and the healthy tissues in a human head phantom have been assessed by means of Monte Carlo simulations. The identification of safe dose limits is carried out by evaluating the maximum peak and valley doses achievable in the tumour while keeping the valley doses in the healthy tissues under tolerances. As the skull receives a significant fraction of the dose, the dose limits are referred to this tissue. Dose distributions with high spatial resolution are presented for various tumour positions, skull thicknesses and interbeam separations. Considering a unidirectional irradiation (field size of 2×2 cm2) and a centrally located tumour, the largest peak and valley doses achievable in the tumour are 55Gy and 2.6Gy, respectively. The corresponding maximum valley doses received by the skin, bone and healthy brain are 4 Gy, 14 Gy and 7 Gy (doses in one fraction), respectively, i.e. within tolerances (5% probability of complication within 5 years).Postprint (published version

Experimental and theoretical L-subshell ionization cross sections for 83Bi by electron impact from the L3 threshold to 100 keV

We report experimental and theoretical Bi L1, L2, and L3 subshell ionization cross sections by the impact of electrons with energies from the Bi L3 ionization threshold to 100 keV. The x-ray spectra have been acquired with two Si drift detectors placed in vacuum, which allowed us to better evaluate the peak fit procedure in the L multiplet. The Lα, Lβ, Lγ, Lℓ, and Lη x-ray production cross sections, measured with relative uncertainties ranging from 5% to 9%, and two sets of atomic relaxation parameters have been used to derive the Bi L1, L2, and L3 ionization cross sections. Although the experimental uncertainties of the subshell ionization cross sections are smaller than those of the few previous measurements, they remain large due to the uncertainties associated with the relaxation parameters. Furthermore, ionization cross sections have been calculated for the three L subshells with the subconfiguration average distorted-wave (SCADW) formalism, which includes the full two-body retarded electromagnetic interaction between the projectile and target electrons. These theoretical cross sections are 15% to 30% lower than the measured values, but the agreement is reasonable given the aforementioned high uncertainties. We have also found that the simpler distorted-wave Born approximation yields subshell ionization cross sections that match those computed with the SCADW method

Monte Carlo Simulation of Electron Backscattering in Solids Using a General-Purpose Computer Code

A Monte Carlo study of backscattering of kilovolt electrons in solids, a process of primary importance in electron microscopy and surface analytical techniques, is carried out. Simulations have been performed using the general-purpose simulation code PENELOPE (an acronym for Penetration and ENErgy LOss of Positrons and Electrons ), which generates electron-photon showers in arbitrary materials. A systematic comparison of results from PENELOPE with available experimental data, and with results from simulations with a much more sophisticated code, is given for electron beams with energies between 2.5 and 60 keV and elemental solids with atomic numbers Z = 4 to 92. It is concluded that PENELOPE gives a reliable description of the backscattering process, even for relatively low electron energies and thin targets