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G Verdú

Publications and source records attributed to G Verdú.

14 recordsLinked to original sources
PubMed2005

Use of risk projection models to estimate mortality and incidence from radiation-induced breast cancer in screening programs.

The authors report on a method to calculate radiological risks, applicable to breast screening programs and other controlled medical exposures to ionizing radiation. In particular, it has been applied to make a risk assessment in the Valencian Breast Cancer Early Detection Program (VBCEDP) in Spain. This method is based on a parametric approach, through Markov processes, of hazard functions for radio-induced breast cancer incidence and mortality, with mean glandular breast dose, attained age and age-at-exposure as covariates. Excess relative risk functions of breast cancer mortality have been obtained from two different case-control studies exposed to ionizing radiation, with different follow-up time: the Canadian Fluoroscopy Cohort Study (1950--1987) and the Life Span Study (1950--1985 and 1950--1990), whereas relative risk functions for incidence have been obtained from the Life Span Study (1958--1993), the Massachusetts tuberculosis cohorts (1926--1985 and 1970--1985), the New York post-partum mastitis patients (1930--1981) and the Swedish benign breast disease cohort (1958--1987). Relative risks from these cohorts have been transported to the target population undergoing screening in the Valencian Community, a region in Spain with about four and a half million inhabitants. The SCREENRISK software has been developed to estimate radiological detriments in breast screening. Some hypotheses corresponding to different screening conditions have been considered in order to estimate the total risk associated with a woman who takes part in all screening rounds. In the case of the VBCEDP, the total radio-induced risk probability for fatal breast cancer is in a range between [5 x 10(-6), 6 x 10(-4)] versus the natural rate of dying from breast cancer in the Valencian Community which is 9.2 x 10(-3). The results show that these indicators could be included in quality control tests and could be adequate for making comparisons between several screening programs.

Adult↗
PubMed2005

Modelling of the mammographic exposure conditions for radiological detriment study in the Valencian Breast Cancer Screening Programme.

Breast screening programmes are the best weapon to fight against breast cancer. Nevertheless, despite the benefits, this practice supposes a radiological risk that cannot be forgotten. In order to calculate breast glandular doses, different MCNP-4C2 models have been developed, simulating the exposure conditions. Radiological detriments have been transported from the population under study in the UNSCEAR 2000 to the Valencian Community, obtaining the detection-induced cancer ratio (DICR) for this population.

Adult↗
PubMed2005

Assessment by cytogenetic analysis of the radioprotection properties of propolis extract.

Propolis obtained from honeybee hives has been used in folk medicine as an anti-inflammatory, anti-carcinogenic or immunomodulatory agent. In animal studies, the radioprotector effect of propolis has been attributed to its free-radical scavenging properties. The present study was carried out to show the protective properties of propolis extract against DNA damage induced by gamma irradiation. The evaluation of the radioprotective effect of propolis has been carried out by the analysis of chromosome aberration induction after several doses of gamma rays. The results of an analysis in the presence of ethanol extract of propolis (EEP) were compared with the dose-effect calibration curve for gamma-rays by analysis of chromosome aberrations without propolis, a decrease in the radiation-induced chromosome aberrations has been observed to be higher than 50% for all the doses.

Cells, Cultured↗
PubMed2005

Declassification of radioactive liquid wastes generated in radio immune assay [corrected] (RIA) laboratories.

Radioactive liquid wastes of low-medium activity level are generated in radio immune assay (RIA) laboratories, which are also potentially infectious because of the pathogens from patient blood. The most common way of managing these wastes consists of a temporal storage, for partial radioactivity decay, followed by management by an authorised company. The object of this work is to study the viability of treating radioactive liquid wastes coming from RIA using membrane techniques in order to reduce their volume, which would mean an improvement from the radiological point of view and a decrease in management costs. This paper describes the results of some experiments carried out with RIA real wastes, by means of processes such as ultrafiltration and reverse osmosis. It has been proved that waste volume can be significantly reduced, obtaining a treated liquid that is free of pathogens and organic matter and with an activity level around the environmental background.

Laboratories, Hospital↗
PubMed2005

MCNP simulation of a Theratron 780 radiotherapy unit.

A Theratron 780 (MDS Nordion) 60Co radiotherapy unit has been simulated with the Monte Carlo code MCNP. The unit has been realistically modelled: the cylindrical source capsule and its housing, the rectangular collimator system, both the primary and secondary jaws and the air gaps between the components. Different collimator openings, ranging from 5 x 5 cm2 to 20 x 20 cm2 (narrow and broad beams) at a source-surface distance equal to 80 cm have been used during the study. In the present work, we have calculated spectra as a function of field size. A study of the variation of the electron contamination of the 60Co beam has also been performed.

Algorithms↗
PubMed2005

A comparative study of computer assisted assessment of image quality index for mammographic phantom images.

Mammographic phantom images are usually used to study the quality of images obtained by dedicated mammographic equipment. The digital image treatment techniques allow us to carry out an automatic analysis of the phantom image. In this work, some techniques of digital image processing are applied to compute a specific image quality index (IQI) for a mammographic phantom, namely CIRS model 11A version SP01. The algorithm designed analyses the phantom image by means of automatic detection of the number of microcalcifications, and the image resolution as the number of line pairs per millimetre. Then, the IQI is calculated from a scoring system. The manner in which the functioning conditions (kV and mAs) of the mammographic equipment and the preprocessing denoising method of the digital image affect the results for the IQI are also studied.

Algorithms↗
PubMed2005

Assessment of mammography spectra using compton spectrometry techniques.

The quality control of mammography units is necessary to reduce the dose imparted to women as much as possible. An accurate characterisation of the primary X-ray spectra is very useful for this purpose. Primary spectra can be obtained using Compton spectrometry techniques. In this work, a commercial spectrometer used to characterise a mammography X-ray tube has been simulated using the Monte Carlo method by means of the MCNP code. Using the developed model, a Response matrix is obtained. Owing to the fact that this matrix is ill-conditioned, the inversion is not a simple process. This problem has been solved using the truncated singular value decomposition method. Results obtained when this methodology was applied have been compared with theoretical X-ray spectra.

Body Burden↗
PubMed2005

Analysis of shielding materials in a Compton spectrometer applied to x-ray tube quality control using Monte Carlo simulation.

A realistic characterisation of the primary beam is very important for the quality control of X-ray tubes. The most accurate technique to assess the actual photon spectrum is X-ray spectrometry. Some difficulties arising in the spectrum determination can be avoided using a Compton spectrometer. Simulation models are useful tools to know the effect of some operational parameters, such as collimation of primary beam, relative position of focus and detector, and the influence of shielding materials. A simulation model has been developed using the MCNP code, based on the Monte Carlo method, in order to reproduce a commercial Compton spectrometer. In this work, the model developed is applied to analyse the influence on measurements of shielding materials present in the spectrometer.

Computer Simulation↗
PubMed2005

Biological dosimetry in a group of radiologists by the analysis of dicentrics and translocations.

The results of a cytogenetic study carried out in a group of nine radiologists are presented. Chromosome aberrations were detected by fluorescence plus Giemsa staining and fluorescence in situ hybridization. Dose estimates were obtained by extrapolating the yield of dicentrics and translocations to their respective dose-effect curves. In seven individuals, the 95% confidence limits of the doses estimated by dicentrics did not include 0 Gy. The 99 dicentrics observed in 17,626 cells gave a collective estimated dose of 115 mGy (95% confidence limits 73-171). For translocations, five individuals had estimated doses that were clearly higher than the total accumulated recorded dose. The 82 total apparently simple translocations observed in 9722 cells gave a collective estimated dose of 275 mGy (132-496). The mean genomic frequencies (x100 +/- SE) of complete and total apparently simple translocations observed in the group of radiologists (1.91 +/- 0.30 and 2.67 +/- 0.34, respectively) were significantly higher than those observed in a matched control group (0.53 +/- 0.10 and 0.87 +/- 0.13, P < 0.01 in both cases) and in another occupationally exposed matched group (0.79 +/- 0.12 and 1.14 +/-0.14, P < 0.03 and P < 0.01, respectively). The discrepancies observed between the physically recorded doses and the biologically estimated doses indicate that the radiologists did not always wear their dosimeters or that the dosimeters were not always in the radiation field.

Adult↗
PubMed2004

Monte Carlo evaluation of kerma in an HDR brachytherapy bunker.

In recent years, the use of high dose rate (HDR) after-loader machines has greatly increased due to the shift from traditional Cs-137/Ir-192 low dose rate (LDR) to HDR brachytherapy. The method used to calculate the required concrete and, where appropriate, lead shielding in the door is based on analytical methods provided by documents published by the ICRP, the IAEA and the NCRP. The purpose of this study is to perform a more realistic kerma evaluation at the entrance maze door of an HDR bunker using the Monte Carlo code GEANT4. The Monte Carlo results were validated experimentally. The spectrum at the maze entrance door, obtained with Monte Carlo, has an average energy of about 110 keV, maintaining a similar value along the length of the maze. The comparison of results from the aforementioned values with the Monte Carlo ones shows that results obtained using the albedo coefficient from the ICRP document more closely match those given by the Monte Carlo method, although the maximum value given by MC calculations is 30% greater.

Brachytherapy↗
PubMed2004

Automatic evaluation of the image quality of a mammographic phantom.

In this work a method has been developed to analyse the digital image quality of a mammographic phantom by means of automatic process techniques. The techniques used for the digital image treatment are standard techniques as the image thresholding to detect objects, the regional growing for pixels pooling and the morphological operator application to determine the objects shape and size, etc. This study allows the obtention of information about the phantom characteristics, that due to its small size and lowly contrast can be obtained very difficultly by direct observation. The final aim of this work is to obtain one or more parameters to characterize the reference phantom quality image in an objective way. These parameters will serve to compare images obtained at different mammographic centers and also, to study the temporal evolution of the image quality produced by determined mammographic equipment.

Algorithms↗
PubMed2004

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

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.

Algorithms↗
PubMed2001

Study of radiation induced cancers in a breast screening programme.

It is demonstrated that screening mammography programmes reduce breast cancer mortality considerably. Nevertheless, radiology techniques have an intrinsic risk, the most important being the late somatic effect of the induction of cancer. This study was carried out in order to evaluate the risk to the population produced by the Comunidad Valenciana Breast Screening Programme. All the calculations are carried out for two risk models, UNSCEAR 94 and NRPB 93. On the one hand, screening series detriments are investigated as a function of doses delivered and other parameters related to population structure and X ray equipment. On the other hand the radiation induced cancer probability for a woman who starts at 45 years and remains in the programme until 65 years old is calculated as a function of mammography units' doses and average compression breast thickness. Finally, risk comparison between a screening programme starting at 45 years old and another one starting at 50 years old is made.

Aged↗