Time filter

Source Type

Correa N.L.,State Institute of Diabetes and Endocrinology IEDE | De Sa L.V.,Brazilian Radiological Protection and Dosimetry Institute (IRD) | De Mello R.C.R.,Federal University of Rio de Janeiro
Thyroid | Year: 2017

Background: An increase in the incidence of second primary cancers is the late effect of greatest concern that could occur in differentiated thyroid carcinoma (DTC) patients treated with radioactive iodine (RAI). The decision to treat a patient with RAI should therefore incorporate a careful risk-benefit analysis. The objective of this work was to adapt the risk-estimation models developed by the Biological Effects of Ionizing Radiation Committee to local epidemiological characteristics in order to assess the carcinogenesis risk from radiation in a population of Brazilian DTC patients treated with RAI. Absorbed radiation doses in critical organs were also estimated to determine whether they exceeded the thresholds for deterministic effects. Methods: A total of 416 DTC patients treated with RAI were retrospectively studied. Four organs were selected for absorbed dose estimation and subsequent calculation of carcinogenic risk: the kidney, stomach, salivary glands, and bone marrow. Absorbed doses were calculated by dose factors (absorbed dose per unit activity administered) previously established and based on standard human models. The lifetime attributable risk (LAR) of incidence of cancer as a function of age, sex, and organ-specific dose was estimated, relating it to the activity of RAI administered in the initial treatment. Results: The salivary glands received the greatest absorbed doses of radiation, followed by the stomach, kidney, and bone marrow. None of these, however, surpassed the threshold for deterministic effects for a single administration of RAI. Younger patients received the same level of absorbed dose in the critical organs as older patients did. The lifetime attributable risk for stomach cancer incidence was by far the highest, followed in descending order by salivary-gland cancer, leukemia, and kidney cancer. Conclusion: RAI in a single administration is safe in terms of deterministic effects because even high-administered activities do not result in absorbed doses that exceed the thresholds for significant tissue reactions. The Biological Effects of Ionizing Radiation Committee mathematical models are a practical method of quantifying the risks of a second primary cancer, demonstrating a marked decrease in risk for younger patients with the administration of lower RAI activities and suggesting that only the smallest activities necessary to promote an effective ablation should be administered in low-risk DTC patients. © Copyright 2017, Mary Ann Liebert, Inc.

Gloor M.,University of Leeds | Brienen R.J.W.,University of Leeds | Galbraith D.,University of Leeds | Feldpausch T.R.,University of Leeds | And 5 more authors.
Geophysical Research Letters | Year: 2013

The Amazon basin hosts half the planet's remaining moist tropical forests, but they may be threatened in a warming world. Nevertheless, climate model predictions vary from rapid drying to modest wetting. Here we report that the catchment of the world's largest river is experiencing a substantial wetting trend since approximately 1990. This intensification of the hydrological cycle is concentrated overwhelmingly in the wet season driving progressively greater differences in Amazon peak and minimum flows. The onset of the trend coincides with the onset of an upward trend in tropical Atlantic sea surface temperatures (SST). This positive longer-term correlation contrasts with the short-term, negative response of basin-wide precipitation to positive anomalies in tropical North Atlantic SST, which are driven by temporary shifts in the intertropical convergence zone position. We propose that the Amazon precipitation changes since 1990 are instead related to increasing atmospheric water vapor import from the warming tropical Atlantic. Key PointsIntensification of Amazon Hydrological Cycle since 1990Revealed by both river discharge and precipitation recordsIn parallel onset of tropical Atlantic warming offering explanation ©2013. American Geophysical Union. All Rights Reserved.

de Paiva E.,Brazilian Radiological Protection and Dosimetry Institute (IRD)
Journal of applied clinical medical physics / American College of Medical Physics | Year: 2011

The Brazilian Institute of Radiation Protection and Dosimetry (IRD/CNEN) carried out quality assurance regulatory audits in Brazilian radiotherapy facilities from 1995 to 2007. In this work, the set of data collected from 195 radiotherapy facilities that use high-energy photon beams are analyzed. They include results from audits in linear electron accelerators and/or Co-60 units. The inspectors of IRD/CNEN performed the dosimetry of high-energy radiotherapy photon beams according to the IAEA dosimetry protocols TRS 277 and TRS 398, and the values of measurements were compared to stated values. Other aspects of radiological protection were checked during on-site audits such as calibration certification of clinical dosimeters and portable monitors, existence and use of check source, use of barometer and thermometer, individual dose registry and training of staff. It was verified that no check source was available in 38% of the visited facilities; the training of personnel was not adequate in 9% of the facilities and the registry of accumulated individual doses was not being done in 6% of the facilities. Measurements of absorbed dose have indicated deviations in the range ± 3% for 67.6% of the cobalt-60 units and 79.6% of medical linear accelerators; 18.5% of Co-60 irradiators and 9.6% of linear accelerators presented deviations in the range 3% < δ ≤ 5%. Finally, 13.9% of Co-60 facilities and 10.8% of linear accelerator facilities presented dosimetry deviations above 5%. The effort in dosimetric quality control performed by IRD/CNEN audits has yielded positive changes that make radiation treatment facilities more reliable.

Sanders C.J.,Federal University of Fluminense | Smoak J.M.,University of South Florida | Naidu A.S.,University of Alaska Fairbanks | Sanders L.M.,Brazilian Radiological Protection and Dosimetry Institute (IRD) | Patchineelam S.R.,Federal University of Fluminense
Estuarine, Coastal and Shelf Science | Year: 2010

The flux of total organic carbon (TOC) to depositional facies (intertidal mud flat, margin and forest) was quantified for a tropical mangrove forest in Brazil. Results indicate that these mangrove margins and intertidal mudflats are sites of large TOC accumulation, almost four times greater than the global averages for mangrove forests. The TOC burial rates were determined from organic carbon content in sediment cores which were dated using 210Pb. Burial rates were calculated to be 1129, 949, and 353 (g m-2 yr-1), for the mud flat, margin and forest, respectively. Sediment accumulation rates (SAR) were estimated to be 7.3, 5.0 and 2.8 mm yr-1. Sediment characterization (δ13C, δ15N, TOC/TN and mud fraction) indicated a representative mangrove system with a record of consistent organic matter flux of up to 100 years. Because of substantial burial of organic carbon in mangrove ecosystems, their role in the global carbon budget must be considered. More importantly, as climate change influences temperature and sea level, mangrove ecosystems will respond to specific climatic conditions. © 2010 Elsevier Ltd.

De Paiva E.,Brazilian Radiological Protection and Dosimetry Institute (IRD)
Results in Physics | Year: 2015

Concave beta sources of 106Ru/106Rh are used in radiotherapy to treat ophthalmic tumors. However, a problem that arises is the difficult determination of absorbed dose distributions around such sources mainly because of the small range of the electrons and the steep dose gradients. In this sense, numerical methods have been developed to calculate the dose distributions around the beta applicators. In this work a simple code in Fortran language is developed to estimate the dose rates along the central axis of 106Ru/106Rh curved plaques by numerical integration of the beta point source function and results are compared with other calculated data. © 2015 The Author.

Conti C.C.,Brazilian Radiological Protection and Dosimetry Institute (IRD) | Salinas I.C.P.,Brazilian Radiological Protection and Dosimetry Institute (IRD) | Zylberberg H.,Brazilian Radiological Protection and Dosimetry Institute (IRD)
Progress in Nuclear Energy | Year: 2013

Due to its high resolution, HPGe detectors are widely used for analysis of gamma emitters radioisotopes. The determination of the response curves for this type of detector is not easy and demands a large number of gamma emitters in order to account for the energy range of interest. For volumetric geometries, a standard solution of a mix of radionuclides is commonly used, but requires one standard solution for each counting geometry of interest. The Monte Carlo method can be used to determine the detector's response curves, making it easier and cheaper. This work presents a detailed description of the procedure to simulate and calibrate co-axial HPGe detectors. It also presents a complete input file for the MCNP5 computer code. The comparison of the simulated and the experimental data showed very good agreement and the discrepancies are mainly due to the uncorrected peak sum effect of the experimental data. © 2013 Elsevier Ltd. All rights reserved.

da Rosa L.A.,Brazilian Radiological Protection and Dosimetry Institute (IRD)
Journal of applied clinical medical physics / American College of Medical Physics | Year: 2010

The purpose of this study is to investigate the influence of lung heterogeneity inside a soft tissue phantom on percentage depth dose (PDD). PDD curves were obtained experimentally using LiF:Mg,Ti (TLD-100) thermoluminescent detectors and applying Eclipse treatment planning system algorithms Batho, modified Batho (M-Batho or BMod), equivalent TAR (E-TAR or EQTAR), and anisotropic analytical algorithm (AAA) for a 15 MV photon beam and field sizes of 1 x 1, 2 x 2, 5 x 5, and 10 x 10 cm 2 . Monte Carlo simulations were performed using the DOSRZnrc user code of EGSnrc. The experimental results agree with Monte Carlo simulations for all irradiation field sizes. Comparisons with Monte Carlo calculations show that the AAA algorithm provides the best simulations of PDD curves for all field sizes investigated. However, even this algorithm cannot accurately predict PDD values in the lung for field sizes of 1 x 1 and 2 x 2 cm 2 . An overdosage in the lung of about 40% and 20% is calculated by the AAA algorithm close to the interface soft tissue/lung for 1 x 1 and 2 x 2 cm 2 field sizes, respectively. It was demonstrated that differences of 100% between Monte Carlo results and the algorithms Batho, modified Batho, and equivalent TAR responses may exist inside the lung region for the 1 x 1 cm 2 field.

de Paiva E.,Brazilian Radiological Protection and Dosimetry Institute (IRD)
Revista Brasileira de Ensino de Fisica | Year: 2014

Radiotherapy is a medical practice that uses ionising radiation for the treatment of cancer. A problem of this type of use of ionizing radiation is how to prevent that the vicinities of the treatment room receive an amount of radiation above the permitted levels. In this work the inverse-square law and the exponential attenuation law of the radiation intensity are used to obtain a basic expression necessary to estimate the thickness of primary barriers in radiotherapy. © by the Sociedade Brasileira de Física.

de Paiva E.,Brazilian Radiological Protection and Dosimetry Institute (IRD)
Revista Brasileira de Ensino de Fisica | Year: 2014

The physicist Arthur Holly Compton used the quantum theory to explain how the scattering of light quantum by electrons takes place, a phenomenon known as Compton effect. An interesting feature of the Compton effect occurs in a frontal collision between the photon and the electron with the photon being backscattered, in which case the energy of the scattered photon is maximum and can be even of the order of magnitude of the energy of the incident electron. Photon beams produced by inverse Compton scattering of laser light by relativistic electrons have scientific, technological, industrial and medical applications. © by the Sociedade Brasileira de Física.

Santo A.S.E.,Brazilian Radiological Protection and Dosimetry Institute (IRD) | Wasserman F.G.,Brazilian Radiological Protection and Dosimetry Institute (IRD) | Conti C.C.,Brazilian Radiological Protection and Dosimetry Institute (IRD)
Annals of Nuclear Energy | Year: 2012

The determination of response curves for HPGe detector demand a large number of gamma sources in order to account for the energy range of interest for a given counting geometry. HPGe well detectors present an additional difficulty, related to the large sum effect for sources placed inside the well, either limiting the useful sources or large analytical corrections, which might imply in large uncertainties. The Monte Carlo method can be used to determine a detector's response curves which are difficult to obtain experimentally. The MCNP5 computer code provides means to simulate gamma ray detectors and has been used for this work for the 50-2000 keV energy range. The detector's sensitive volume was determined by comparison of simulated and measured spectra due to two point sources, 241Am and 137Cs. The thickness of the dead layer + transition layer was determined for all crystal's surfaces, and the response curves for two volumetric sources geometries, one placed on top of the detector and a smaller one placed inside the well, were then obtained by simulation and compared with the experimental results, in order to verify and validate the detector's simulation. Both simulated and experimental response curves were in very good agreement. © 2012 Elsevier Ltd. All rights reserved.

Loading Brazilian Radiological Protection and Dosimetry Institute (IRD) collaborators
Loading Brazilian Radiological Protection and Dosimetry Institute (IRD) collaborators