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Da Rosa L.A.R.,Brazilian Radiological Protection and Dosimetry Institute (IRD) | Facure A.,Brazilian National Nuclear Energy Commission
Radiation Physics and Chemistry

Concave eye applicators with 90Sr/90Y and 106Ru/106Rh beta-ray sources are usually used in brachytherapy for the treatment of superficial intraocular tumors as uveal melanoma with thickness up to 5mm. The aim of this work consisted in using the Monte Carlo code MCNPX to calculate the 3D dose distribution on a mathematical model of the human eye, considering 90Sr/90Y and 160Ru/160Rh beta-ray eye applicators, in order to treat a posterior uveal melanoma with a thickness 3.8mm from the choroid surface. Mathematical models were developed for the two ophthalmic applicators, CGD produced by BEBIG Company and SIA.6 produced by the Amersham Company, with activities 1mCi and 4.23mCi respectively. They have a concave form. These applicators' mathematical models were attached to the eye model and the dose distributions were calculated using the MCNPX *F8 tally. The average doses rates were determined in all regions of the eye model. The *F8 tally results showed that the deposited energy due to the applicator with the radionuclide 106Ru/106Rh is higher in all eye regions, including tumor. However the average dose rate in the tumor region is higher for the applicator with 90Sr/90Y, due to its high activity. Due to the dosimetric characteristics of these applicators, the PDD value for 3mm water is 73% for the 106Ru/106Rh applicator and 60% for 90Sr/90Y applicator. For a better choice of the applicator type and radionuclide it is important to know the thickness of the tumor and its location. © 2013 Elsevier Ltd. Source

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

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. Source

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

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. Source

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

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. Source

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

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. Source

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