Programas de Monitoramento Ambiental aplicados na Sub-Região Baixo Tapajós e Vale do Jamanxim, estado do Pará

The study area of this work includes two sub-regions covered by the BR-163 road, which is Baixo Tapajós and Vale do Jamanxim. This region was monitored from Environmental Monitoring Programs of the Federal Government. This study presents results of anthropism data from ProAE 2012 for Special Areas and deforestation data from PRODES / INPE 2011 applied to the remainder. After structuring the database, software R 2.13.2 was used to generate histogram of frequency of the investigated variables (anthropism, roads and drainage), from synchronization with the database created in Terra View 4.1.0. Non-Special Areas represents 43,7% of the investigated area, and according PRODES 2011 presents 1.212.693,00 hectares of deforestation accumulated, that is, 20,00% of total. Special Areas occupies 57,3% of the investigated territory, and ProAE 2012 identified 319.320,76 hectares of anthropism, which equates to 3,92%. The frequency histograms: percentage of anthropism, presence of roads and drainage, for Special and Non-Special Areas, pointed to the same pattern between anthropism and roads, rather than drainage. Despite anthropism rates are lower within the Special Areas, there is still a high human pressure therein, as it presents ProAE 2012 results. These protected areas are forest, mineral and biodiversity reserve, bringing the challenge consolidation of environmental management in this region.Pages: 6853-686

Angular distribution of bremsstrahlung from 15-MeV electrons incident on thick targets of Be, Al, and Pb

Bremsstrahlung spectra from thick cylindrical targets of Be, Al, and Pb have been measured at angles of 0°, 1°, 2°, 4°, 10°, 30°, 60°, and 90° relative to the beam axis for electrons of 15-MeV incident energy. The spectra are absolute (photons per incident electron) and have a 145-keV lower-energy cutoff. The target thicknesses were nominally 110% of the electron CSDA range. A thin transmission detector, calibrated against a toroidal current monitor, was placed upstream of the target to measure the beam current. The spectrometer was a 20-cm-diam by 25-cm-long cylindrical Nal detector. Measured spectra were corrected for pile-up, background, detector response, detector efficiency, attenuation in materials between the target and detector and collimator effects. Spectra were also calculated using the EGS4 Monte Carlo system for simulating the radiation transport. There was excellent agreement between the measured and calculated spectral shapes. The measured yield of photons per incident electron was 9% and 7% greater than the calculated yield for Be and Al, respectively, and 2% less for Pb, all with an uncertainty of ±5%. There was no significant angular variation in the ratio of the measured and calculated yields. The angular distributions of bremsstrahlung calculated using available analytical theories dropped off more quickly with angle than the measured distributions. The predictions of the theories would be improved by including target-scattered photons

Report of the AAPM Task Group No. 105: Issues associated with clinical implementation of Monte Carlo-based photon and electron external beam treatment planning

The Monte Carlo (MC) method has been shown through many research studies to calculate accurate dose distributions for clinical radiotherapy, particularly in heterogeneous patient tissues where the effects of electron transport cannot be accurately handled with conventional, deterministic dose algorithms. Despite its proven accuracy and the potential for improved dose distributions to influence treatment outcomes, the long calculation times previously associated with MC simulation rendered this method impractical for routine clinical treatment planning. However, the development of faster codes optimized for radiotherapy calculations and improvements in computer processor technology have substantially reduced calculation times to, in some instances, within minutes on a single processor. These advances have motivated several major treatment planning system vendors to embark upon the path of MC techniques. Several commercial vendors have already released or are currently in the process of releasing MC algorithms for photon and/or electron beam treatment planning. Consequently, the accessibility and use of MC treatment planning algorithms may well become widespread in the radiotherapy community. With MC simulation, dose is computed stochastically using first principles; this method is therefore quite different from conventional dose algorithms. Issues such as statistical uncertainties, the use of variance reduction techniques, theability to account for geometric details in the accelerator treatment head simulation, and other features, are all unique components of a MC treatment planning algorithm. Successful implementation by the clinical physicist of such a system will require an understanding of the basic principles of MC techniques. The purpose of this report, while providing education and review on the use of MC simulation in radiotherapy planning, is to set out, for both users and developers, the salient issues associated with clinical implementation and experimental verification of MC dose algorithms. As the MC method is an emerging technology, this report is not meant to be prescriptive. Rather, it is intended as a preliminary report to review the tenets of the MC method and to provide the framework upon which to build a comprehensive program for commissioning and routine quality assurance of MC-based treatment planning systems