An international survey of imaging practices in radiotherapy.

Improvements in delivery of radiation dose to target tissues in radiotherapy have increased the need for better image quality and led to a higher frequency of imaging patients. Imaging for treatment planning extends to function and motion assessment and devices are incorporated into medical linear accelerators (linacs) so that regions of tissue can be imaged at time of treatment delivery to ensure dose distributions are delivered as accurately as possible. A survey of imaging in 97 radiotherapy centres in nine countries on six continents has been undertaken with an on-line questionnaire administered through the International Commission on Radiological Protection mentorship programme to provide a snapshot of imaging practices. Responses show that all centres use CT for planning treatments and many utilise additional information from magnetic resonance imaging and positron emission tomography scans. Most centres have kV cone beam CT attached to at least some linacs and use this for the majority of treatment fractions. The imaging options available declined with the human development index (HDI) of the country, and the frequency of imaging during treatment depended more on country than treatment site with countries having lower HDIs imaging less frequently. The country with the lowest HDI had few kV imaging facilities and relied on MV planar imaging intermittently during treatment. Imaging protocols supplied by vendors are used in most centres and under half adapt exposure conditions to individual patients. Recording of patient doses, a knowledge of which is important in optimisation of imaging protocols, was limited primarily to European countries.

First Report of Stewart's Wilt of Maize in Argentina Caused by Pantoea stewartii.

Stewart's wilt is a serious disease of corn (Zea mays L.) caused by the bacterium Pantoea stewartii subsp. stewartii (Pss). Typical symptoms of infected fields and dent corn are longitudinal streaks with irregular or wavy margins, which are parallel to the veins and may extend the length of the leaf. These pale to green yellow lesions become dry and brown as the disease progresses producing a leaf blight (4). During the growing seasons 2010 to 2011 and 2011 to 2012, symptoms of bacterial leaf blight of corn were observed in central Argentina maize fields, with an incidence of 54% in Córdoba province. To identify the pathogen, leaves from 10 symptomatic maize plants per field were collected from 15 fields covering a representative geographical area. High populations of morphologically uniform bacteria were isolated from leaf tissues by conventional methods using King's medium B agar (2). Ten representative facultatively anaerobic gram-negative, non-fluorescing, non-motile, catalase positive and oxidase negative rod-shaped and yellow-pigmented bacterial isolates were evaluated further. The biochemical profile obtained was: fermentative metabolism, negative indol, acetoin and hydrogen sulfide production, negative gelatin hydrolysis (22°C), positive acid production from D-glucose and lactose, negative gas production from D-glucose, and negative nitrate reduction (1). All the isolates produced a 300-bp band with PCR using the species specific primer pair PST3581/PST3909c (3). The Pss ATCC 8199 and Pseudomonas fluorescens ATCC 13525 strains were used as positive and negative controls for the PCR assays, respectively. The pathogenicity test was performed by stem inoculation of five to ten P2069 YR maize plants (one to two leaf growth stage) grown in growth chamber. Plants were inoculated by syringe with a 107 to 108 cell/ml bacterial suspension and kept in a humid chamber at 25 to 27°C. Plants inoculated with Pss ATCC 8199 or with sterile water were used as positive and negative control treatments, respectively. The development of symptoms similar to those originally found in the field was observed on all the plants inoculated with the different isolates at 7 to 10 days post inoculation. In addition, symptoms on inoculated plants were similar to those observed for the positive control treatment. No symptoms were found on negative controls. Koch's postulates were fulfilled since bacteria isolated from symptomatic tissue had identical characteristics to isolates used to inoculate plants and to the reference Pss strain for biochemical tests and PCR reaction mentioned above. To our knowledge, this is the first report of P. stewartii subsp. stewartii isolated from diseased maize in Argentina. References: (1) J. G. Holt et al. Page 179 in: Bergey's manual of determinative bacteriology. Williams and Wilkins, Baltimore, MD, 1994. (2) OEPP/EPPO. Bulletin OEPP/EPPO Bulletin, 36: 111, 2006. Pantoea stewartii subsp. stewartii diagnostic. (3) A. Wensing et al. Appl. Environ. Microbiol. 76:6248, 2010. (4) D. G. White Page 4 in: Compendium of corn disease. The American Phytopathology Society, 1999.

Caracterización de un nuevo material para uso como tejido sustituto en radioterapía / Caracteristcs of material new for use with tejido substitute in rediotherapy

Introducción:Dada la necesidad de un material que reiniera las características apropiadas para se utilizado como tejido sustituto en la práctica de la radioterapía, se elaboró un material con base en tejido blando de pescado, agua y glicerina. Objetivos:Describir la caracterización dosimétrica y química para determinar la viabilidad de la utilización como maniquí o bolus. Matriales, métodos y resultados: eL material, no es degradable por la radiaación, es reciclable y además tiene una composición elemental muy cercana a la ideal. Debido a que su origen es un tejido animal, se encontraron proporciones relativamente altas de silicio y calcio que podrían disminuirse. El análisis dosimétrico se realizó con radiación gamma (Co-60) y rayos de alta energ1a (6MV) midiendo los coeficientyes de atenuación lineal y los porcentajes de dosis en profundidad. En los coeficientes de atenuación lineal se encontró una relación con respecto al agua de 0,990, para Co-60 y de 0,987 para 6MV. Conclusiones: la densidad electrónica y la dosis en profundidad, de acuerdo con los resultados obtenidos, presentan ventajas respecto a otros materiales utilizados convencionalmente.

The influence of arc weights on the dose distribution for single target radiosurgery.

To stereotactically irradiate ellipsoidal inclined arteriovenous malformations (AVMs) with a single isocenter one can use an adjusted inclined irradiation space with a reduced angular range of arcs. If one uses the maximum available irradiation space it is necessary to weight some of the arcs in order to closely encompass the lesion. It has been found that there is a relationship between the lesion inclination angle beta and the weights of arcs. Conversely when the beta angle is known, the weights of the arcs can be determined in advance by means of weighting vectors. The dose volume analysis shows that the isodose volumes remain constant for the different weighting vectors except for the 10% isodose volume which increases slightly as the linear weighting vector's slope alpha increases. Moreover, this procedure permits the optimization of the superimposition between the lesion and the reference isodose. These results enable the construction of an "a priori knowledge" database that can be included in an optimization algorithm procedure.