Sergio Gallardo

Bio: Sergio Gallardo is an academic researcher from Polytechnic University of Valencia. The author has contributed to research in topics: Monte Carlo method & Detector. The author has an hindex of 9, co-authored 68 publications receiving 315 citations.

Application of the Monte Carlo method to the analysis of measurement geometries for the calibration of a HP Ge detector in an environmental radioactivity laboratory

Abstract: A gamma spectrometer including an HP Ge detector is commonly used for environmental radioactivity measurements. The efficiency of the detector should be calibrated for each geometry considered. Simulation of the calibration procedure with a validated computer program is an important auxiliary tool for environmental radioactivity laboratories. The MCNP code based on the Monte Carlo method has been applied to simulate the detection process in order to obtain spectrum peaks and determine the efficiency curve for each modelled geometry. The source used for measurements was a calibration mixed radionuclide gamma reference solution, covering a wide energy range (50–2000 keV). Two measurement geometries – Marinelli beaker and Petri boxes – as well as different materials – water, charcoal, sand – containing the source have been considered. Results obtained from the Monte Carlo model have been compared with experimental measurements in the laboratory in order to validate the model.

Monte carlo simulation of the compton scattering technique applied to characterize diagnostic x-ray spectra.

Abstract: The quality control of x-ray tubes for medical radiodiagnostic services is very important for such devices. Therefore, the development of new procedures to characterize the x-ray primary beam is highly interesting in order to obtain an accurate assessment of the actual photon spectrum. The Compton scattering technique is very useful to determine x-ray spectra (in the 10-150 kVp range), avoiding a pile-up effect in the detector since a large room is not usually available to apply other techniques. In this work, this process has been simulated using a Monte Carlo code, MCNP 4C. Some geometrical models have been developed and different techniques have been studied in order to improve statistics and accuracy in the acquisition of Pulse Height Distribution (PHD). The effect of both the collimation of the primary beam and the scattering angle of the spectrometer has been analyzed. Results obtained using simulation models have been compared with experimental measurements.

X-ray spectrum unfolding using a regularized truncated SVD method

Abstract: New procedures to characterize the x-ray primary beam, obtaining an accurate assessment of the actual photon spectrum, are needed for quality control of x-ray tubes for medical purposes. The Compton scattering technique is very useful for determining x-ray spectra (in the 10–150 kVp range), avoiding the pile-up effect in the detector, since usually there is insufficient space available to apply other techniques. The Compton scattering procedure was simulated using the Monte Carlo method by means of the MCNP code. In order to validate the simulation model, experimental measurements were made at the Centro Nacional de Dosimetria (CND), Valencia, Spain, using a calibrated x-ray tube. Different spectra were measured varying the operational parameters (kV, mA, Al). Furthermore, CND provided the theoretical spectra corresponding to the x-ray measurement conditions. Using the developed model, a response matrix was obtained by simulating the interactions of different monoenergetic beams. During the construction of the primary photon spectrum it is necessary to calculate the inverse of the response matrix. Because this matrix is ill-conditioned, its inversion is not a simple process. This problem was solved using a truncated singular value decomposition (TSVD), method together with variational regularization. The performance of the methodology was tested with experimental and simulated x-ray spectra. Copyright © 2005 John Wiley & Sons, Ltd.

Calculated and measured brachytherapy dosimetry parameters in water for the Xoft Axxent X-Ray Source: an electronic brachytherapy source.

Abstract: A new x-ray source, the model S700 Axxent X-Ray Source (Source), has been developed by Xoft Inc. for electronic brachytherapy. Unlike brachytherapy sources containing radionuclides, this Source may be turned on and off at will and may be operated at variable currents and voltages to change the dose rate and penetration properties. The in-water dosimetry parameters for this electronic brachytherapy source have been determined from measurements and calculations at 40, 45, and 50 kV settings. Monte Carlo simulations of radiation transport utilized the MCNP5 code and the EPDL97-based mcplib04 cross-section library. Inter-tube consistency was assessed for 20 different Sources, measured with a PTW 34013 ionization chamber. As the Source is intended to be used for a maximum of ten treatment fractions, tube stability was also assessed. Photon spectra were measured using a high-purity germanium (HPGe) detector, and calculated using MCNP. Parameters used in the two-dimensional (2D) brachytherapy dosimetry formalism were determined. While the Source was characterized as a point due to the small anode size, < 1 mm, use of the one-dimensional (1D) brachytherapy dosimetry formalism is not recommended due to polar anisotropy. Consequently, 1D brachytherapy dosimetry parameters were not sought. Calculated point-source model radial dose functions at gP(5) were 0.20, 0.24, and 0.29 for the 40, 45, and 50 kV voltage settings, respectively. For 1

Task-based measures of image quality and their relation to radiation dose and patient risk

Abstract: The theory of task-based assessment of image quality is reviewed in the context of imaging with ionizing radiation, and objective figures of merit (FOMs) for image quality are summarized. The variation of the FOMs with the task, the observer and especially with the mean number of photons recorded in the image is discussed. Then various standard methods for specifying radiation dose are reviewed and related to the mean number of photons in the image and hence to image quality. Current knowledge of the relation between local radiation dose and the risk of various adverse effects is summarized, and some graphical depictions of the tradeoffs between image quality and risk are introduced. Then various dose-reduction strategies are discussed in terms of their effect on task-based measures of image quality.

Available online a t www.pelagiaresearchlibrary.com

Abstract: Caesarean section rates are inexorably rising which has led to the possibility of negative impact on m aternal and neonatal health. Present study was aimed to compare the factors associated with caesarean and vaginal births among pregnant women. A retrospective study was con ducted in Obstetrics and Gynaecology Department, Pu njab Institute of Medical Sciences, Jalandhar (Punjab, Iduring the period of April, 2012 to June, 201 2. Details of age group, parity, socioeconomic status, antenatal booking, mode of delivery, obstetric complications, gestational age at delivery, maternal and neonatal outcomes wer e explored. The prevalence of Caesarean Sections (6 5%) was higher over vaginal births (35%). It had higher num ber of Emergency (52.31%) over Elective (47.70%) ca esarean sections. Multiparity (55.38%; p<0.05), high socioe conomic status (18.46%), 21 to 30 yrs of age group (78.46%) and booked status (44.62%) were associated with Cae sarean Sections while primiparity (65.71%) and low socioeconomic status (22.86%) with vaginal births. The commonest reasons for Caesarean Sections were F etal Distress (30.77%) and Repeat Caesarean Sections (29.23%). Ca esarean sections rate is high. High number of referred patients who underwent Emergency sections was the main reason. Trial of vaginal birth after C aesarean Section in approximate cases and confirmation of su spected fetal distress through fetal blood acid bas e study are recommended.