220 research outputs found

    Dosimetric evaluation of Acuros XB Advanced Dose Calculation algorithm in heterogeneous media

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    <p>Abstract</p> <p>Background</p> <p>A study was realised to evaluate and determine relative figures of merit of a new algorithm for photon dose calculation when applied to inhomogeneous media.</p> <p>Methods</p> <p>The new Acuros XB algorithm implemented in the Varian Eclipse treatment planning system was compared against a Monte Carlo method (VMC++), and the Analytical Anisotropic Algorithm (AAA). The study was carried out in virtual phantoms characterized by simple geometrical structures. An insert of different material and density was included in a phantom built of skeletal-muscle and HU = 0 (setting "A"): Normal Lung (lung, 0.198 g/cm<sup>3</sup>); Light Lung (lung, 0.035 g/cm<sup>3</sup>); Bone (bone, 1.798 g/cm<sup>3</sup>); another phantom (setting "B") was built of adipose material and including thin layers of bone (1.85 g/cm<sup>3</sup>), adipose (0.92 g/cm<sup>3</sup>), cartilage (1.4745 g/cm<sup>3</sup>), air (0.0012 g/cm<sup>3</sup>). Investigations were performed for 6 and 15 MV photon beams, and for a large (13 × 13 cm<sup>2</sup>) and a small (2.8 × 13 cm<sup>2</sup>) field.</p> <p>Results</p> <p>Results are provided in terms of depth dose curves, transverse profiles and Gamma analysis (3 mm/3% and 2 mm/2% distance to agreement/dose difference criteria) in planes parallel to the beam central axis; Monte Carlo simulations were assumed as reference. Acuros XB gave an average gamma agreement, with a 3 mm/3% criteria, of 100%, 86% and 100% for Normal Lung, Light Lung and Bone settings, respectively, and dose to medium calculations. The same figures were 86%, 11% and 100% for AAA, where only dose rescaled to water calculations are possible.</p> <p>Conclusions</p> <p>In conclusion, Acuros XB algorithm provides a valid and accurate alternative to Monte Carlo calculations for heterogeneity management.</p

    Testing the portal imager GLAaS algorithm for machine quality assurance

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    <p>Abstract</p> <p>Background</p> <p>To report about enhancements introduced in the GLAaS calibration method to convert raw portal imaging images into absolute dose matrices and to report about application of GLAaS to routine radiation tests for linac quality assurance procedures programmes.</p> <p>Methods</p> <p>Two characteristic effects limiting the general applicability of portal imaging based dosimetry are the over-flattening of images (eliminating the "horns" and "holes" in the beam profiles induced by the presence of flattening filters) and the excess of backscattered radiation originated by the detector robotic arm supports. These two effects were corrected for in the new version of GLAaS formalism and results are presented to prove the improvements for different beams, detectors and support arms. GLAaS was also tested for independence from dose rate (fundamental to measure dynamic wedges).</p> <p>With the new corrections, it is possible to use GLAaS to perform standard tasks of linac quality assurance. Data were acquired to analyse open and wedged fields (mechanical and dynamic) in terms of output factors, MU/Gy, wedge factors, profile penumbrae, symmetry and homogeneity. In addition also 2D Gamma Evaluation was applied to measurement to expand the standard QA methods. GLAaS based data were compared against calculations on the treatment planning system (the Varian Eclipse) and against ion chamber measurements as consolidated benchmark. Measurements were performed mostly on 6 MV beams from Varian linacs. Detectors were the PV-as500/IAS2 and the PV-as1000/IAS3 equipped with either the robotic R- or Exact- arms.</p> <p>Results</p> <p>Corrections for flattening filter and arm backscattering were successfully tested. Percentage difference between PV-GLAaS measurements and Eclipse calculations relative doses at the 80% of the field size, for square and rectangular fields larger than 5 × 5 cm<sup>2 </sup>showed a maximum range variation of -1.4%, + 1.7% with a mean variation of <0.5%. For output factors, average percentage difference between GLAaS and Eclipse (or ion chamber) data was -0.4 ± 0.7 (-0.2 ± 0.4) respectively on square fields. Minimum, maximum and average percentage difference between GLAaS and Eclipse (or ion chamber) data in the flattened field region were: 0.1 ± 1.0, 0.7 ± 0.8, 0.1 ± 0.4 (1.0 ± 1.4, -0.3 ± 0.2, -0.1 ± 0.2) respectively. Similar minimal deviations were observed for flatness and symmetry.</p> <p>For Dynamic wedges, percentage difference of MU/Gy between GLAaS and Eclipse (or ion chamber) was: -1.1 ± 1.6 (0.4 ± 0.7). Minimum, maximum and average percentage difference between GLAaS and Eclipse (or ion chamber) data in the flattened field region were: 0.4 ± 1.6, -1.5 ± 1.8, -0.1 ± 0.3 (-2.2 ± 2.3, 2.3 ± 1.2, 0.8 ± 0.3) respectively.</p> <p>For mechanical wedges differences of transmission factors were <1.6% (Eclipse) and <1.1% (ion chamber) for all wedges. Minimum, maximum and average percentage difference between GLAaS and Eclipse (or ion chamber) data in the flattened field region were: -1.3 ± 0.7, -0.7 ± 0.7, -0.2 ± 0.2 (-0.8 ± 0.8, 0.7 ± 1.1, 0.2 ± 0.3) respectively.</p> <p>Conclusion</p> <p>GLAaS includes now efficient methods to correct for missing "horns" and "holes" induced by flattening filter in the beam and to compensate for excessive backscattering from the support arm. These enhancements allowed to use GLAaS based dosimetric measurement to perform standard tasks of Linac quality assurance with reliable and consistent results. This fast method could be applied to routine practice being also fast in usage and because it allows the introduction of new analysis tools in routine QA by means, e.g., of the Gamma Index analysis.</p

    Comparison of biological and reproductive parameters between Helicoverpa zea and Helicoverpa arm¡gera in Argentina.

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    Conteúdo do volume 2: Ácaros; Biologia, fisiologia, morfologia; Controle biológico com bactérias entomopatogênicas; Controle biológico com fungos entomopatológicos; Controle biológico com nematoides; Controle biológico com parasitoides; Controle biológico com predadores; Ecologia e biodiversidade; Educação e etnoentomologia; Entomologia florestal; Entomologia Forense; Entomologia médica e veterinária; Entomologia molecular; Manejo integrado de pragas; Organismos geneticamente modificados; Plantas inseticidas; Polinização; Pragas quarentenárias e invasivas; Resistência de insetos a táticas de controle; Resistência de plantas a insetos; Semioquímicos e comportamento; Sistemática e taxonomia; Tecnologia de aplicação; Controle biológico com vírus entomopatogênicos; Controle químico

    Early clinical experience of radiotherapy of prostate cancer with volumetric modulated arc therapy

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    <p>Abstract</p> <p>Background</p> <p>To report about initial clinical experience in radiation treatment of carcinoma of prostate with volumetric modulated arcs with the RapidArc (RA) technology.</p> <p>Methods</p> <p>Forty-five patients with a median age of 72 ± 3, affected by prostate carcinoma (T1c: 22 patients, T2a-b: 17 patients, T3a-b: 6 patients. N0: 43 patients, N1-Nx: 2 patients, all M0), with initial PSA of 10.0 ± 3.0 ng/mL, were treated with RapidArc in a feasibility study. All patients were treated with single arc using 6MV photons. Dose prescription ranged between 76 (7 patients) and 78 Gy (38 patients) in 2Gy/fraction. Plan quality was assessed by means of Dose Volume Histogram (DVH) analysis. Technical parameters of arcs and pre-treatment quality assurance results (Gamma Agreement Index, GAI) are reported to describe delivery features. Early toxicity was scored (according to the Common Terminology Criteria of Adverse Effects scale, CTCAE, scale) at the end of treatment together with biochemical outcome (PSA).</p> <p>Results</p> <p>From DVH data, target coverage was fulfilling planning objectives: V<sub>95% </sub>was in average higher than 98% and V<sub>107%</sub>~0.0% (D<sub>2%</sub>~104.0% in average). Homogeneity D<sub>5%</sub>-D<sub>95% </sub>ranged between 6.2 ± 1.0% to 6.7 ± 1.3%. For rectum, all planning objectives were largely met (e.g. V<sub>70Gy </sub>= 10.7 ± 5.5% against an objective of < 25%) similarly for bladder (e.g. D<sub>2% </sub>= 79.4 ± 1.2Gy against an objective of 80.0Gy). Maximum dose to femurs was D<sub>2% </sub>= 36.7 ± 5.4Gy against an objective of 47Gy. Monitor Units resulted: MU/Gy = 239 ± 37. Average beam on time was 1.24 ± 0.0 minutes. Pre-treatment GAI resulted in 98.1 ± 1.1%. Clinical data were recorded as PSA at 6 weeks after RT, with median values of 0.4 ± 0.4 ng/mL. Concerning acute toxicity, no patient showed grade 2-3 rectal toxicity; 5/42 (12%) patients experienced grade 2 dysuria; 18/41 (44%) patients preserved complete or partial erectile function.</p> <p>Conclusion</p> <p>RapidArc proved to be a safe, qualitative and advantageous treatment modality for prostate cancer.</p

    Critical appraisal of the role of volumetric modulated arc therapy in the radiation therapy management of breast cancer

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    Background: The aim of this review is the critical appraisal of the current use of volumetric modulated arc therapy for the radiation therapy management of breast cancer. Both clinical and treatment planning studies were investigated. Material and methods: A Pubmed/MEDLINE search of the National Library of Medicine was performed to identify VMAT and breast related articles. After a first order rejection of the irrelevant findings, the remaining articles were grouped according to two main categories: clinical vs. planning studies and to some sub-categories (pointing to significant technical features). Main areas of application, dosimetric and clinical findings as well as areas of innovations were defined. Results: A total of 131 articles were identified and of these, 67 passed a first order selection. Six studies reported clinical results while 61 treatment dealed with treatment planning investigations. Among the innovation lines, the use of high intensity photon beams (flattening filter free), altered fractionation schemes (simultaneous integrated boost, accelerated partial breast irradiation, single fraction), prone positioning and modification of standard VMAT (use of dynamic trajectories or hybrid VMAT methods) resulted among the main relevant fields of interest. Approximately 10% of the publications reported upon respiratory gating in conjunction with VMAT. Conclusions: The role of VMAT in the radiation treatment of breast cancer seems to be consolidated in the in-silico arena while still limited evidence and only one phase II trial appeared in literature from the clinical viewpoint. More clinical reports are needed to fully proove the expected dosimetric benefits demonstrated in the planning investigations

    Relevamiento de cítricos del Noroeste Argentino (NOA) para la detección de Xylella fastidiosa, agente causal de CVC

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    La clorosis variegada de los cítricos (CVC), causada por la bacteria Xylella fastidiosa subsp.  pauca, afecta  principalmente naranja Valencia, Pera, Hamlin y Natal. Se detectó en Brasil en 1987 y en la Argentina, en 1984 en Misiones y 1990 en Corrientes, ambas provincias del Noreste Argentino (NEA). En el NOA, si bien no se han observado síntomas sospechosos, no existían hasta el presente reportes de análisis de muestras en laboratorio. Considerando el antecedente de detección de la bacteria en hojas asintomáticas de cítricos en Misiones, se realizó un relevamiento para determinar si X. fastidiosaestá presente en los cítricos del NOA. Personal de la EEAOC y SENASA recorrió lotes de naranja Valencia y limón de Tucumán, Salta, Jujuy y Catamarca, cuyas plantas tenían tres a diez años de edad, rango óptimo para detectar CVC. En cada lote se inspeccionó el 50% de las plantas y se extrajeron muestras de hojas del 10% del total de plantas del mismo. Se recolectaron 4186 muestras, 2277 procedentes de Salta y Jujuy (767 de limón, 1444 de naranja, 65 de mandarina y 1 de pomelo), 65 de Catamarca (18 de limón y 47 de naranja) y 1844 de Tucumán (1106 de limón, 733 de naranja dulce y 5 de mandarina). Se analizaron las muestras por PCR con los cebadores específicos para la bacteria (CVC-1 y 272-2i). Todas las muestras analizadas resultaron negativas. Hasta el presente no hay evidencias de que la bacteria causante del CVC esté presente en los cítricos del NOA.Fil: Fogliata, G. M.. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; ArgentinaFil: Acosta, M. E.. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; ArgentinaFil: Martinez, C. V.. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; ArgentinaFil: Rojas, A, A.. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; ArgentinaFil: Sanchez, Leandro Arturo. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; Argentina2º Congreso Argentino De FitopatologíaMar del PlataArgentinaAsociación Argentina de Fitopatólogo
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