A thin target approach for portal imaging in medical accelerators

A new thin-target method (patent pending) is described for portal imaging with low-energy (tens of keV) photons from a medical linear accelerator operating in a special mode. Low-energy photons are usually produced in the accelerator target, but are absorbed by the target and flattening filter, both made of medium- or high- Z materials such as Cu or W. Since the main contributor to absorption of the low-energy photons is self-absorption by the thick target through the photoelectric effect, it is proposed to lower the thickness of the portal imaging target to the minimum required to get the maximum low-energy photon fluence on the exit side of the target, and to lower the atomic number of the target so that predominantly photoelectric absorption is reduced. To determine the minimum thickness of the target, EGS4 Monte Carlo calculations were performed. As a result of these calculations, it was concluded that the maximum photon fluence for a 4 MeV electron beam is obtained with a 1.5 mm Cu target. This value is approximately five times less than the thickness of the Cu target routinely used for bremsstrahlung production in radiotherapeutic practice. Two sets of experiments were performed: the first with a 1.5 mm Cu target and the second with a 5 mm Al target (Cu mass equivalent) installed in the linear accelerator. Portal films were taken with a Rando anthropomorphic phantom. To emphasize the low-energy response of the new thin target we used a Kodak Min-R mammographic film and cassette combination, with a strong low-energy response. Because of its high sensitivity, only 1 cGy is required. The new portal images show a remarkable improvement in sharpness and contrast in anatomical detail compared with existing ones. It is also shown that further lowering of the target's atomic number (for example to C or Be) produces no significant improvement.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48963/2/m80816.pd

Sunscreens - Which and what for?

It is well established that sun exposure is the main cause for the development of skin cancer. Chronic continuous UV radiation is believed to induce malignant melanoma, whereas intermittent high-dose UV exposure contributes to the occurrence of actinic keratosis as precursor lesions of squamous cell carcinoma as well as basal cell carcinoma. Not only photocarcinogenesis but also the mechanisms of photoaging have recently become apparent. In this respect the use of sunscreens seemed to prove to be more and more important and popular within the last decades. However, there is still inconsistency about the usefulness of sunscreens. Several studies show that inadequate use and incomplete UV spectrum efficacy may compromise protection more than previously expected. The sunscreen market is crowded by numerous products. Inorganic sunscreens such as zinc oxide and titanium oxide have a wide spectral range of activity compared to most of the organic sunscreen products. It is not uncommon for organic sunscreens to cause photocontact allergy, but their cosmetic acceptability is still superior to the one given by inorganic sunscreens. Recently, modern galenic approaches such as micronization and encapsulation allow the development of high-quality inorganic sunscreens. The potential systemic toxicity of organic sunscreens has lately primarily been discussed controversially in public, and several studies show contradictory results. Although a matter of debate, at present the sun protection factor (SPF) is the most reliable information for the consumer as a measure of sunscreen filter efficacy. In this context additional tests have been introduced for the evaluation of not only the protective effect against erythema but also protection against UV-induced immunological and mutational effects. Recently, combinations of UV filters with agents active in DNA repair have been introduced in order to improve photoprotection. This article reviews the efficacy of sunscreens in the prevention of epithelial and nonepithelial skin cancer, the effect on immunosuppression and the value of the SPF as well as new developments on the sunscreen market. Copyright (C) 2005 S. Karger AG, Basel

Ploidia de DNA em astrocitomas: estudo em 66 pacientes brasileiros DNA ploidy in glioma: study in 66 Brazilian patients

A determinação do conteúdo de DNA nuclear (fração de fase S e ploidia de DNA) foi realizada por meio de análise de imagem em 66 astrocitomas, a partir de material fixado em formalina e seccionado em cortes de 5 micrômetros corados pela técnica de Feulgen. Nossos resultados mostraram forte relação entre a idade do paciente, grau histológico e sobrevida , com a ploidia de DNA e o percentual de células em fase de síntese. A análise da atividade proliferativa de astrocitomas intracranianos é a nosso ver muito útil no entendimento do comportamento biológico , do prognóstico e para o planejamento terapêutico dessas lesões.<br>The determination of the nuclear DNA content (S-phase fraction (SPF) and ploidy) was carried out by image analysis (IA). The morphometric and densitometric features of Feulgen-stained nuclei were determined from stored formalin-fixed and paraffin-embedded specimens of 66 patients with intracranial astrocytomas. Our results suggest a strong relationship between patient age, histological grade,survival and DNA ploidy and SPF. The analysis of the proliferative activity of intracranial astrocytomas is very helpfull in understanding biological stractification and prognostication to assess tumor behaviour and planning of treatment strategies

Avaliação de iniciativas e programas intersetoriais em saúde: desafios e aprendizados Evaluation of initiatives and intersectorial programs in health: challenges and learning

O objetivo deste artigo é contribuir para a avaliação das iniciativas voltadas para a construção de arranjos intersetoriais no âmbito das políticas públicas de saúde e de proteção social. São tomados como focos analíticos a iniciativa de Desenvolvimento Local Integrado e Sustentável de Manguinhos (DLIS-Manguinhos) - uma proposta de base territorial e comunitária associada à estratégias de colaboração e negociação bottom up- e a experiência de implementação do programa federal de transferência condicionada de renda Bolsa Família (PBF). Nesta perspectiva, aspectos ligados às redes de mobilização social, perfil dos atores envolvidos, tipos de incentivos e níveis de integração institucional são tratados como elementos cruciais para a análise do alcance de programas e iniciativas que articulam propostas intersetoriais. Conclui-se que a interface e o diálogo entre pesquisa, avaliação e acompanhamento de processos decisórios constituem eixos centrais para o maior aprendizado social e institucional na área.<br>The objective of his article is to contribute to the evaluation of the initiatives aimed at the creation of intersectorial arrangements in the scope of public health policies and social protection. The focus is on the Integrated and Sustainable Local Development of Manguinhos (DLIS-Manguinhos) - a territory and community based proposal associated to bottom up cooperation and negotiation strategies - and the experience of establishing the conditioned cash transference federal program called Bolsa Família (Family Grant Program - PBF). In this perspective, the aspects related to social mobilization networks, profile of the players involved, types of incentive and levels of institutional integration are treated as crucial elements in the analysis of the programs and initiatives that articulate intersectorial proposals. It is concluded that the interface and dialog among research, evaluation and follow up of decision processes constitute the central axes for better social and institutional learning in the area