Conformal proton radiation therapy requires accurate prediction of the Bragg peak position. Protons may be more suitable than conventional x rays for this task since the relative electron density distribution can be measured directly with proton computed tomography ͑CT͒. However, proton CT has its own limitations, which need to be carefully studied before this technique can be introduced into routine clinical practice. In this work, we have used analytical relationships as well as the Monte Carlo simulation tool GEANT4 to study the principal resolution limits of proton CT. The noise level observed in proton CT images of a cylindrical water phantom with embedded tissueequivalent density inhomogeneities, which were generated based on GEANT4 simulations, compared well with predictions based on Tschalar's theory of energy loss straggling. The relationship between phantom thickness, initial energy, and the relative electron density resolution was systematically investigated to estimate the proton dose needed to obtain a given density resolution. We show that a reasonable density resolution can be achieved with a relatively small dose, which is comparable to or even lower than that of x-ray CT.

The use of protons instead of X-rays for computerized tomography (CT) studies has potential advantages, especially for medical applications in proton treatment planning. However, the spatial resolution of proton CT is limited by multiple Coulomb scattering (MCS). We used the Monte Carlo simulation tool GEANT4 to study the resolution achievable with different experimental arrangements of a proton CT scanner. The passage of a parallel 200MeV proton beam through a virtual cylindrical aluminum phantom with 50mm external diameter was simulated. In our study, the phantom contained a set of cylindrical holes with diameters ranging from 4mm to 0.5mm. The GEANT4 simulation consisted of a series of 180 projections at 2 degree intervals with 350 proton track histories for each one. The fi ltered back projection algorithm was used to reconstruct a 2D tomographic image of phantom.

In existing proton treatment centers, dose calculations are performed based on x-ray computerized tomography (CT). Alternatively, the therapeutic proton beam could be used to collect the data for treatment planning via proton CT (pCT). With the development of medical proton gantries, first at Loma Linda University Medical Center and now in several other proton treatment centers, it is of interest to continue the early pCT investigations of the 1970s and the early 1980s. From that time, the basic idea of the pCT method has advanced from average energy loss measurements to an individual proton tracking technique. This reduces the image degradation due to multiple Coulomb scattering. Thereby, the central pCT problem shifts to the fidelity of the physical information obtained about the scanned patient, which will be used for proton treatment planning. The accuracy of relative electron density distributions extracted from pCT images was investigated in this work using continuous slowing down approximation (CSDA) and water-equivalent-thickness (WET) concepts. Analytical results were checked against Monte Carlo simulations, which were obtained with SRIM2003 and GEANT4 Monte Carlo software packages. The range of applications and the sources of absolute errors are discussed.

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Este estudo levantou dados buscando caracterizar o perfil clínico de ambientes escolares (escolas e centros educacionais) os quais apresentaram índices elevados de Poluição Sonora Ambiente no município de Paranaguá/PR. As ações fizeram parte da integração entre a universidade e a Secretaria Estadual de Educação (NRE Paranaguá– PR). A ideia central visou mensurar a intensidade sonora (em dB) com equipamento de medição (decibelímetro), bem como comparar com valores de referência já estabelecidos no Brasil (Inmetro) e no mundo (OMS). Os dados foram coletados na Escola Arthur de Miranda Ramos, por duas acadêmicas (Graduação em Fisioterapia e em Saúde Coletiva), participantes do projeto de Iniciação Científica, para posterior integração das ações socioeducativas e de saúde. Este estudo também visa mapear o perfil dos sintomas auditivos dos profissionais, buscando soluções diagnósticas para eventuais problemas, trazendo à tona a realidade desta situação e principalmente as possíveis soluções como, por exemplo, encaminhamento para exame de caráter otológico, mudança de layout nas salas de aula e medidas educacionais de controle dos níveis de ruído. A intensidade sonora quando excessiva pode trazer danos irreparáveis ao ouvido humano, observando-se sintomas auditivos, vestibulares, vocais, psicológicos, cardiológicos, entre outros. Os níveis de ruído acústico em ambientes escolares foram medidos e correlacionados com os sintomas e queixas apresentados pelos indivíduos desta comunidade (alunos, professores, serventes, etc.) durante as conversas e reuniões. Os níveis de ruído encontrados foram excessivos e provavelmente apresentam insalubridade para a qualidade de vida desta comunidade escolar. Os resultados apresentados são todos acima de 70 dB, sendo assim já apresentam risco elevado às condições de saúde dos alunos e dos profissionais.