General Purpose Transistor Characterized as Dosimetry Sensor of Proton Beams.

A commercial pMOS transistor (MOSFET), 3N163 from Vishay (USA), has been characterized as a low-energy proton beam dosimeter. The top of the samples' housing has been removed to guarantee that protons reached the sensitive area, that is, the silicon die. Irradiations took place at the National Accelerator Centre (Seville, Spain). During irradiations, the transistors were biased to improve the sensitivity, and the silicon temperature was monitored activating the parasitic diode of the MOSFET. Bias voltages of 0, 1, 5, and 10 V were applied to four sets of three transistors, obtaining an averaged sensitivity that was linearly dependent on this voltage. In addition, the short-fading effect was studied, and the uncertainty of this effect was obtained. The bias voltage that provided an acceptable sensitivity, (11.4 ± 0.9) mV/Gy, minimizing the uncertainty due to the fading effect (-0.09 ± 0.11) Gy was 1 V for a total absorbed dose of 40 Gy. Therefore, this off-the-shelf electronic device presents promising characteristics as a dosimeter sensor for proton beams.

Monte Carlo calculation of charge collection efficiencies in ionization chambers.

Collection efficiency is an important quantity in dosimetry with ionization chambers. It can be calculated by solving a hyperbolic system of partial differential equations. This system can be solved only in few, simple, idealized geometries, but for more realistic designs an analytical resolution is no longer possible. In the present work a Monte Carlo scheme that could permit to calculate the collection efficiency for any ionization chamber geometry is proposed. This scheme has been tested against Boag's approach for three chambers with plane-parallel, cylindrical and spherical geometries, operated in the recombination regime. The results obtained in the full Monte Carlo simulation closely agree with the Boag's ones for the three ideal geometries considered. The largest relative difference, ∼0.3%, has been found for the plane-parallel chamber in case of 50 V, the lowest potential difference investigated in this study. Results appear to be stable against changes in the chamber volume, the ion mobility and the recombination constant. The method proposed could be a useful tool to calculate collection efficiencies of ionization chambers, provided the electric field inside them is known.

Quality indexes based on water measurements for low and medium energy x-ray beams: a theoretical study with PENELOPE.

PURPOSE: To study the use of quality indexes based on ratios of absorbed doses in water at two different depths to characterize x-ray beams of low and medium energies. METHODS: A total of 55 x-ray beam spectra were generated with the codes XCOMP5R and SPEKCALC and used as input of a series of Monte Carlo simulations performed with PENELOPE, in which the percentage depth doses in water and the kQ,Q0 factors, defined in the TRS-398 protocol, were determined for each beam. Some of these calculations were performed by simulating the ionization chamber PTW 30010. RESULTS: The authors found that the relation between kQ,Q0 and the ratios of absorbed doses at two depths is almost linear. A set of ratios statistically compatible with that showing the best fit has been determined. CONCLUSIONS: The results of this study point out which of these ratios of absorbed doses in water could be used to better characterize x-ray beams of low and medium energies.

Hiperactividad vesical con incontinencia urinaria: trece años de calvario / No disponible

La International Continent Society define la incontinencia urinaria (IU) como una situación en que la pérdida involuntaria de orina a través de la uretra, demostrable objetivamente, genera un problema social e higiénico. Esta representa una patología compleja y de difícil solución. El impacto sobre la calidad de vida de la IU es superior a otras patologías crónicas, como la hipertensión o la diabetes; deteriora la calidad de vida, reduce la autoestima, teniendo graves repercusiones psicológicas y sociales. Este artículo presenta el caso clínico de una paciente con hiperactividad vesical e incontinencia urinaria, que durante trece años ve alterada su vida por esta patología (AU)

The International Continent Society defines urinary incontinence (UI) as a situation in that the involuntary loss of urine through the urethra, provable objectively, generates a social and hygienic problem. It represents a complex pathology and of difficult solution. The impact on the quality of life of the UI is superior to other chronic pathologies, as hypertension or the diabetes; it deteriorates the quality of life, reduces self-esteem, having severe psychological and social repercussions. This article presents the clinical case of a patient with vesical hyperactivity and urinary incontinence, who during thirteen years sees her life altered by this pathology (AU)

A simple analytical expression to calculate the backscatter factor for low energy X-ray beams.

A simple analytical expression aiming to calculate the backscatter factor used in dosimetry protocols to determine the absorbed dose in water for low energy X-rays beams is presented. This expression is based on the linear dependence of the backscatter factor with the generating potential, for fixed values of the half-value layer. The results of a recent work in which 74 X-ray beams with different spectroscopic characteristics, generated with the code (xcomp5r) and transported with the Monte Carlo code (penelope) have been used. The expression derived permits to calculate the backscatter factor within 5% accuracy. The predictive power of this expression has been tested for 20 X-ray beams generated with potentials from 50 to 250 kV, for which half-value layers and backscatter factors have been experimentally determined.

Monte Carlo simulation using the PENELOPE code with an ant colony algorithm to study MOSFET detectors.

In this work we have developed a simulation tool, based on the PENELOPE code, to study the response of MOSFET devices to irradiation with high-energy photons. The energy deposited in the extremely thin silicon dioxide layer has been calculated. To reduce the statistical uncertainties, an ant colony algorithm has been implemented to drive the application of splitting and Russian roulette as variance reduction techniques. In this way, the uncertainty has been reduced by a factor of approximately 5, while the efficiency is increased by a factor of above 20. As an application, we have studied the dependence of the response of the pMOS transistor 3N163, used as a dosimeter, with the incidence angle of the radiation for three common photons sources used in radiotherapy: a (60)Co Theratron-780 and the 6 and 18 MV beams produced by a Mevatron KDS LINAC. Experimental and simulated results have been obtained for gantry angles of 0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees and 75 degrees. The agreement obtained has permitted validation of the simulation tool. We have studied how to reduce the angular dependence of the MOSFET response by using an additional encapsulation made of brass in the case of the two LINAC qualities considered.

Multiple scattering of 13 and 20 MeV electrons by thin foils: a Monte Carlo study with GEANT, Geant4, and PENELOPE.

PURPOSE: In this work, recent results from experiments and simulations (with EGSnrc) performed by Ross et al. [Med. Phys. 35, 4121-4131 (2008)] on electron scattering by foils of different materials and thicknesses are compared to those obtained using several Monte Carlo codes. METHODS: Three codes have been used: GEANT (version 3.21), Geant4 (version 9.1, patch03), and PENELOPE (version 2006). In the case of PENELOPE, mixed and fully detailed simulations have been carried out. RESULTS: Transverse dose distributions in air have been obtained in order to compare with measurements. The detailed PENELOPE simulations show excellent agreement with experiment. The calculations performed with GEANT and PENELOPE (mixed) agree with experiment within 3% except for the Be foil. In the case of Geant4, the distributions are 5% narrower compared to the experimental ones, though the agreement is very good for the Be foil. Transverse dose distribution in water obtained with PENELOPE (mixed) is 4% wider than those calculated by Ross et al. using EGSnrc and is 1% narrower than the transverse dose distributions in air, as considered in the experiment. CONCLUSIONS: All the codes give a reasonable agreement (within 5%) with the experimental results for all the material and thicknesses studied.

Benchmark of penelope for low and medium energy X-rays.

The Monte Carlo code penelope is benchmarked for X-ray beams with energies between 30 and 300 keV. The results of different simulations performed with penelope are compared with those obtained with a semi-empirical computational model and with experimental measurements. Half-value layer indexes obtained from the attenuation curves for Al and Cu and depth dose curves in water have been considered for this comparison. A good agreement is reached on what guarantees the feasibility of the code.

Study of the formalism used to determine the absorbed dose for low-energy x-ray beams.

We have studied the procedure commonly recommended by dosimetry protocols for the determination of the absorbed dose in water for low-energy x-rays beams, generated with potentials up to 150 kVp. X-ray beams with different spectra obtained with the XCOMP5R code were transported using the Monte Carlo code PENELOPE in order to calculate backscatter factors and mass-energy absorption coefficients. We have analyzed the uncertainty in the absorbed doses, calculated using the half-value layer to characterize the x-ray beams, due to the uncertainties in both backscatter factors and mass-energy absorption coefficients. We have found that this uncertainty is larger than 5% and can reach values above 11% for some HVL(1) values. The characterization of these doses with the homogeneity coefficient or the generating potential, in addition to the half-value layer is also studied. Using HVL(1) and the kVp, the absorbed dose to water can be reproduced to within 3% for all spectra.

Quilotóraz bilateral masivo en postoperatorio de gastrectomía subtotal / Bilateral chylothorax alter gastric surgery

Quilotórax es el acúmulo de linfa en la cavidad pleural por obstrucción o rotura del conducto torácico. La etiología más frecuente es la neoplásica; se relaciona también con traumatismos y iatrogénica. Se presenta el caso de una mujer de 76 años con quilotórax bilateral, predominantemente derecho, durante el postoperatorio de una gastrectomía subtotal. Debutó con clínica de insuficiencia respiratoria y la evolución fue favorable sin precisar tratamiento reparador quirúrgico

Chylothorax is a lymphatic effusion of chylous in the pleural space due to thoracic duct obstruction or injury. The most frequent aetiology is cancer; it is also related to chest trauma and iatrogenic. We describe the case of bilateral chylothorax in a 76-year-old woman, right predominant, during the post-operational phase of gastric surgery. This presented itself with respiratory insufficiency and tachycardia without initial haemodynamic compromise. It presented a favourable evolution after conservative treatment, cessation of oral intake and TPN and chest tube during 10 to 14 days

On the safety assessment of human exposure in the proximity of cellular communications base-station antennas at 900, 1800 and 2170 MHz.

In this work, the procedures for safety assessment in the close proximity of cellular communications base-station antennas at three different frequencies (900, 1800 and 2170 MHz) are analysed. For each operating frequency, we have obtained and compared the distances to the antenna from the exposure places where electromagnetic fields are below reference levels and the distances where the specific absorption rate (SAR) values in an exposed person are below the basic restrictions, according to the European safety guidelines. A high-resolution human body model has been located, in front of each base-station antenna as a worst case, at different distances, to compute whole body averaged SAR and maximum 10 g averaged SAR inside the exposed body. The finite-difference time-domain method has been used for both electromagnetic fields and SAR calculations. This paper shows that, for antenna-body distances in the near zone of the antenna, the fact that averaged field values be below the reference levels could, at certain frequencies, not guarantee guidelines compliance based on basic restrictions.

[Bilateral chylothorax after gastric surgery]. / Quilotórax bilateral masivo en postoperatorio de gastrectomía subtotal.

Chylothorax is a lymphatic effusion of chylous in the pleural space due to thoracic duct obstruction or injury. The most frequent aetiology is cancer; it is also related to chest trauma and iatrogenic. We describe the case of bilateral chylothorax in a 76-year-old woman, right predominant, during the post-operational phase of gastric surgery. This presented itself with respiratory insufficiency and tachycardia without initial haemodynamic compromise. It presented a favourable evolution after conservative treatment, cessation of oral intake and TPN and chest tube during 10 to 14 days.

Comparison of FDTD-calculated specific absorption rate in adults and children when using a mobile phone at 900 and 1800 MHz.

In this paper, the specific absorption rate (SAR) in scaled human head models is analysed to study possible differences between SAR in the heads of adults and children and for assessment of compliance with the international safety guidelines, while using a mobile phone. The finite-difference time-domain method (FDTD) has been used for calculating SAR values for models of both children and adults, at 900 and 1800 MHz. Maximum 1 g averaged SAR (SAR1 g) and maximum 10 g averaged SAR (SAR10 g) have been calculated in adults and scaled head models for comparison and assessment of compliance with ANSI/IEEE and European guidelines. Results show that peak SAR1 g and peak SAR10 g all trend downwards with decreasing head size but as head size decreases, the percentage of energy absorbed in the brain increases. So, higher SAR in children's brains can be expected depending on whether the thickness of their skulls and surrounding tissues actually depends on age. The SAR in eyes of different sizes, as a critical organ, has also been studied and very similar distributions for the full size and the scaled models have been obtained. Standard limits can only be exceeded in the unpractical situation where the antenna is located at a very short distance in front of the eye.

[Renal artery stenosis in the transplant patient]. / Estenosis de la arteria renal en el trasplantado.

OBJECTIVE: To present our experience in the diagnosis and treatment of renal artery stenosis in kidney transplants. METHODS: A review of 601 renal transplants performed in adults showed 32 cases of renal artery stenosis. The diagnostic techniques utilized were arteriography in 18 patients, DIVAS in 15, echo-Doppler in 11 patients and MAG with captopril test on two occasions. RESULTS: Arterial hypertension was the most common symptom (92.8%), alone (53.1%) or in association with impaired renal function (43.7%). 46.8% of the cases could be managed by drug therapy. Percutaneous transluminal angioplasty was performed in 14 patients. Surgery was required on two occasions. CONCLUSIONS: The incidence of renal artery stenosis in our series of renal transplants in adults up to 1997 was 5.3%. Arterial hypertension with or without impairment of renal function was the most common symptom. Currently, echo-doppler and MAG with captopril test are the most widely utilized diagnostic techniques. Percutaneous transluminal angioplasty is the treatment of choice in renal artery stenosis when arterial hypertension is refractory to drug therapy. Good results are achieved in 57%, although it is not free from complications. In case of failure, revascularization surgery is the alternative approach.

Synthesis and amyloid binding properties of rhenium complexes: preliminary progress toward a reagent for SPECT imaging of Alzheimer's disease brain.

The definitive diagnosis of Alzheimer's disease (AD) requires the detection of amyloid plaques in postmortem brain. Although the amount of fibrillar amyloid roughly correlates with the severity of symptoms at the time of death, the temporal relationship between amyloid deposition, neuronal loss, and cognitive decline is unclear. To elucidate this relationship, a noninvasive, practical method for the quantitation of brain amyloid deposition is required. We describe herein the initial stages of a strategy to accomplish this goal by single photon computed tomographic imaging. The amyloid-binding dye Congo Red was modified to allow its conjugation to the monoamine-monoamide bis(thiol) ligand. This ligand complexes technetium(V) in its neutral oxo form. A biphenyl-containing building block was conjugated to the protected ligand, and the product was coupled to the relevant aromatic compounds. Rhenium oxo complexes, which are isosteric, but nonradioactive, analogues of the potential imaging agent technetium oxo complexes, were synthesized. These complexes bound to Abeta amyloid fibrils produced in vitro and stained amyloid plaques and vascular amyloid in AD brain sections.

[Breast metastasis of bladder carcinoma: report of a case]. / Metástasis mamaria de carcinoma vesical: a propósito de un caso.

OBJECTIVE: To report a case of carcinoma of the bladder metastatic to the mammary gland. METHODS: A 72-year-old male with mammary gland metastasis secondary to a bladder carcinoma is described. The more common routes of tumor spread and the approach to these lesions are discussed. CONCLUSIONS: The prognosis for this type of lesion is poor except in a rare few.

[The migration of indigenous mixtecans. Population mobility and preservation of identities]. / La migracion de indigenas mixtecos. Movilidad poblacional y preservacion de identidades.

PIP: In today's world, where large numbers of people migrate for reasons that are not strictly economic, the preservation of the cultural identity of migrants has attracted scrutiny. Indigenous populations are one of the most vulnerable groups in Mexico because of their economic disadvantages and their ethnic identity. Paradoxically, however, their ethnic identity has constituted a basis for preserving their cultural identity and creating a broad network of social relations that assist them in their territorial movement. The Mixtec region of western Oaxaca, Guerrero, and Puebla is one of the poorest of Mexico, with high rates of emigration, infant mortality, and illiteracy, and villages lacking potable water and basic services such as schools and roads. Holdings of less than two hectares of impoverished and eroded lands do not provide resources to support life at even a subsistence level. Migration, a constant in Mixtec economic and social life, accelerated in the 1980s. The Mixtec have become one of the largest ethnic groups of workers in the northwest of Mexico and in California, Oregon, and Washington. Entire communities have migrated in search of work. In their continuous movement the Mixtec have conserved ties that permit their collective survival. Associating with other Mixtec allows the migrants to share food, lodgings, and information on possibilities for success in their search for work. Mixtec families living in Tijuana, for example, assist those staying temporarily in Tijuana on their way elsewhere. The migrants provide their hosts with information about their villages or on conditions elsewhere. The continual movement in search of work has led the Mixtec to establish themselves in Guadalajara, Culiacan, Hermosillo, Nogales, Tijuana, Ensenada, and elsewhere, creating parallel routes north for subsequent migrants. More than 20,000 Mixtec were estimated to be employed in California, Oregon, and Washington in 1990. The Mixtec find temporary work in agriculture but also in small cleaning and maintenance enterprises. In Mexico they work as agricultural laborers or construction workers, domestics or ambulatory vendors. Migration has become an element in the daily life of the Mixtec, who have broadened their horizons while preserving their identity.^ieng