Characterization of a novel proton-CT scanner based on Silicon and LaBr3_3(Ce) detectors

Treatment planning systems at proton-therapy centres generally use X-ray computed tomography (CT) as primary imaging technique to infer the proton treatment doses to tumour and healthy tissues. However, proton stopping powers in the body, as derived from X-ray images, suffer from important proton-range uncertainties. In order to reduce this uncertainty in range, one could use proton-CT images instead. The main goal of this work is to test the capabilities of a newly-developed proton-CT scanner, based on the use of a set of tracking detectors and a high energy resolution scintillator for the residual energy of the protons. Different custom-made phantoms were positioned at the field of view of the scanner and were irradiated with protons at the CCB proton-therapy center in Krakow. We measured with the phantoms at different angles and produced sinograms that were used to obtain reconstructed images by Filtered Back-Projection (FBP). The obtained images were used to determine the capabilities of our scanner in terms of spatial resolution and proton Relative Stopping Power mapping and validate its use as proton-CT scanner. The results show that the scanner can produce medium-high quality images, with spatial resolution better than 2 mm in radiography, below 3 mm in tomography and resolving power in the RSP comparable to other state of the art pCT cameras

Morfologia e produção de grãos em linhagens modernas de feijão-caupi submetidas a diferentes densidades populacionais.

Os progressos na agricultura dependem, em parte, do desenvolvimento de novos genótipos com características que atendam às exigências dos sistemas de cultivo tecnificados. O objetivo deste trabalho foi avaliar os efeitos de diferentes arranjos populacionais sobre características morfológicas e de produção em genótipos modernos de porte ereto e hábito de crescimento determinado. O experimento foi conduzido em 2002, na área experimental da Embrapa - Centro de Pesquisa Agropecuária do Meio-Norte, em Teresina - Piauí, utilizando-se o delineamento experimental de blocos casualizados no esquema fatorial 5x3, com quatro repetições. Os tratamentos foram constituídos por cinco genótipos (IT 87D-611-3, TE 97-411-1F-16, TE 97-406-2F-22-2, EVx 91-2E-2 e TE 96-282-22G) e três populações de plantas ( 105, 3x105 e 5x105 plantas.ha-1). As variáveis analisadas foram: número de nós no ramo principal (NNRP); comprimento do ramo principal (CRP); número de ramos laterais (NRL); peso de 100 grãos (PCG); produção de grãos por planta (PGP) e rendimento de grãos (REND). Aumentos nas densidades de plantas promovem mudanças significativas na morfologia e na capacidade produtiva das plantas com aumento no comprimento do ramo principal e reduções no número de nós do ramo principal, número de ramos laterais e produção de grãos por planta. O maior rendimento de grãos é obtido na população de 3x105 plantas.ha-1

Proton radiographs using position-sensitive silicon detectors and high-resolution scintillators

Proton therapy is a cancer treatment technique currently in growth worldwide. It offers advantages with respect to conventional X-ray and $\gamma$-ray radiotherapy, in particular, a better control of the dose deposition allowing to reach a higher conformity in the treatments. Therefore, it causes less damage to the surrounding healthy tissue and less secondary effects. However, in order to take full advantage of its potential, improvements in treatment planning and dose verification are required. A new prototype of proton Computed Tomography scanner is proposed to design more accurate and precise treatment plans for proton therapy. Here, results obtained from an experiment performed using a 100-MeV proton beam at the CCB facility in Krakow (Poland) are presented. Proton radiographs of PMMA samples of 50-mm thickness with spatial patterns in aluminum were taken. Their properties were studied, including reproduction of the dimensions, spatial resolution and sensitivity to different materials. They demonstrate the capabilities of the system to produce images with protons. Structures of up to 2 mm are nicely resolved and the sensitivity of the system was enough to distinguish thicknesses of 10 mm of aluminum or PMMA. This constitutes a first step to validate the device as a proton radiography scanner previous to the future tests as a proton CT scanner.Comment: 7 pages, 11 figures, submitted to IEEE TNS ANIMMA 2021 Conference Proceeding

Abstracts

Tradução, para a língua inglesa, dos resumos dos artigos publicados nesta edição

Outcome measures associated with perceived stress

We tend to think of situations in life as stressful when they are unpredictable, uncontrollable or overloading. Stress is a very personal experience. Perceived stress is a reflection of how such external stressful events and everyday hassles are ‘filtered’ according to our individual personality traits and coping strategies. People with tinnitus describe various stress-related complaints, but these symptoms are not just restricted to tinnitus. Poor concentration, sense of loss of control, sleep disturbance and irritability are also shared with people who are experiencing a state of generalised anxiety or depression. Whatever their origin, the goal of any clinical intervention for people with tinnitus should be to reduce these negative symptoms. This chapter takes a look at the way in which perceived stress associated with tinnitus has been measured. My focus is on clinical trials, but I start from the perspective of questionnaire construction by describing and comparing tinnitus-specific and general stress measures. I then evaluate how these instruments have been applied in a range of contemporary tinnitus trials. The chapter includes tutorials that introduce the reader to fundamental concepts in clinical trial design, understanding the purpose of questionnaires and appreciating the relevance of sample size calculations

A simulation study of the effect of drift electric fields on the response of radiation detectors using the PENELOPE code

The effect of the presence of a drift electric field on the response of gaseous and semiconductor radiation detectors to energetic X-rays (energies from 20 to 200 keV) is investigated using the PENELOPE code to simulate the photo-absorption and the slow-down of the electrons produced in Si, Ge, and Xe gas at 1 atm. For typical drift fields, the energy deposited in the detection media is calculated taking into account the energy exchanged by the electrons with the field. The analysis of the calculated distributions shows that the effect of the field on the distributions is negligible in Si and Ge semiconductor detectors, but not in Xe gas detectors, where for the fluctuations introduced by the field for approach the intrinsic values for Xe, and the intrinsic discontinuity in linearity when crosses the Xe K-edge (34.56 keV) is further reduced by [approximate]4%. The simulation data also suggest that this field effect may cause some deviations to the expected Gaussian response of Xe detectors to the absorption of monoenergetic photons.http://www.sciencedirect.com/science/article/B6TJM-4JKJSCP-3/1/3af24dda8150f1611ede9a26a32189f