TY - JOUR A1 - Waas, Thomas A1 - Brockmann, R. A1 - Weise, Wolfram T1 - Deeply bound pionic states and the effective pion mass in nuclear systems JF - Physics Letters B N2 - We show that the s-wave pion-nuclear potential which reproduces the deeply bound pionic states in Pb, recently discovered at GSI, is remarkably close to the one constructed directly from low energy theorems based on chiral symmetry. Converting this information into an effective pion mass we find m:/m,, N 1.13 in the center of the Pb nucleus, and mi/m,, N 1.07 in symmetric nuclear matter. Y1 - 1997 U6 - https://doi.org/10.1016/S0370-2693(97)00643-6 N1 - Die Preprint-Version ist ebenfalls in diesem Repositorium verzeichnet unter: VL - 405 IS - 3;4 SP - 215 EP - 218 PB - Elsevier ER - TY - JOUR A1 - Dobler, Barbara A1 - Walter, Cornelia A1 - Knopf, Antje A1 - Fabri, Daniella A1 - Löschel, Rainer A1 - Polednik, Martin A1 - Schneider, Frank A1 - Wenz, Frederik A1 - Lohr, Frank T1 - Optimization of extracranial stereotactic radiation therapy of small lung lesions using accurate dose calculation algorithms JF - Radiation Oncology N2 - BACKGROUND The aim of this study was to compare and to validate different dose calculation algorithms for the use in radiation therapy of small lung lesions and to optimize the treatment planning using accurate dose calculation algorithms. METHODS A 9-field conformal treatment plan was generated on an inhomogeneous phantom with lung mimics and a soft tissue equivalent insert, mimicking a lung tumor. The dose distribution was calculated with the Pencil Beam and Collapsed Cone algorithms implemented in Masterplan (Nucletron) and the Monte Carlo system XVMC and validated using Gafchromic EBT films. Differences in dose distribution were evaluated. The plans were then optimized by adding segments to the outer shell of the target in order to increase the dose near the interface to the lung. RESULTS The Pencil Beam algorithm overestimated the dose by up to 15% compared to the measurements. Collapsed Cone and Monte Carlo predicted the dose more accurately with a maximum difference of -8% and -3% respectively compared to the film. Plan optimization by adding small segments to the peripheral parts of the target, creating a 2-step fluence modulation, allowed to increase target coverage and homogeneity as compared to the uncorrected 9 field plan. CONCLUSION The use of forward 2-step fluence modulation in radiotherapy of small lung lesions allows the improvement of tumor coverage and dose homogeneity as compared to non-modulated treatment plans and may thus help to increase the local tumor control probability. While the Collapsed Cone algorithm is closer to measurements than the Pencil Beam algorithm, both algorithms are limited at tissue/lung interfaces, leaving Monte-Carlo the most accurate algorithm for dose prediction. Y1 - 2006 U6 - https://doi.org/10.1186/1748-717X-1-45 VL - 1 PB - BMC ; Springer ER - TY - JOUR A1 - Zygmanski, Piotr A1 - Högele, Wolfgang A1 - Cormack, Robert A1 - Chin, Lee A1 - Löschel, Rainer T1 - A volumetric-modulated arc therapy using sub-conformal dynamic arc with a monotonic dynamic multileaf collimator modulation JF - Physics in medicine and biology N2 - We present a new dose delivery scheme utilizing sub-conformal dynamic arc (sub-CD-ARC) with a dynamic multileaf collimator (dMLC) modulation in a single rotation. In sub-conformal delivery, a MLC aperture conforms not to the whole target but to its portion, simultaneously completely avoiding organs at risk (OARs). In CD-ARC therapy, the dose deposition level depends on the target width and distance to the axis of rotation, and therefore the use of multiple arcs is necessary to achieve a uniform dose within the target in 3D. In our delivery scheme, the dose deposition variations symptomatic of non-modulating sub-CD-ARC are compensated for in 3D by a quasi-periodic monotonic dMLC modulation. For this reason, we call this scheme sub-conformal dynamic modulated arc (sub-CD-MARC) therapy. The advantage of using such a modulation is that MLC leaf motion has just a few control points, and that an inverse planning problem is reduced to a linear equation problem with a few unknown parameters, which have clear physical meaning. We show the general dosimetric properties of sub-CD-ARC and sub-CD-MARC for a specific geometry of the target and OARs (rotational symmetry with varying inner and outer radii along the axis of rotation). In addition, we present numerical results of sub-CD-MARC inverse planning optimization. Y1 - 2008 U6 - https://doi.org/10.1088/0031-9155/53/22/009 VL - 53 IS - 22 SP - 6395 EP - 6417 PB - IOP Publishing ER - TY - JOUR A1 - Hoegele, W. A1 - Löschel, Rainer A1 - Zygmanski, Piotr T1 - An alternative VMAT with prior knowledge about the type of leaf motion utilizing projection method for concave targets JF - Medical physics N2 - The authors present an alternative approach to inverse planning optimization and apply it to volumetric modulated are therapy (VMAT) in one rotation with a prior knowledge about the type of leaf motions. The optimization is based on the projection theorem in inner product spaces. MLC motion is directly considered in the optimization, thus avoiding leaf segmentation characteristic of IMRT optimization. In this work they realize the method for concave irregular targets encompassing an organ at risk leading to a repetitive MLC motion pattern. Applying the projection theorem leads to a noniterative optimization method and reduces to solving few systems of linear equations with small numbers of dimensions. The solution of the inverse problem is unique, and false minima are naturally excluded. They divided the full rotation into about 50 short arc segments and for each segment decomposed dose into separate contributions related to stages of MLC motion. This results generally in an inverse problem with just four free parameters per arc segment. Practically three degrees of freedom will be used for the purpose of a constant angular speed of the gantry. Therefore the total number of degrees of freedom for a 3D problem is about 3 x 50 x number of collimator leaf pairs for irradiating the whole target volume in one rotation. Two 2D and one 3D concave target volumes are applied for a slice by slice optimization. A 6 MV photon beam model is used, including realistic scattering and attenuation, and a maximal leaf velocity of 3 cm/s is regarded. The resulting dose distributions cover the PTVs very well and have maxima at about 108% of dose in the PTVs. The OAR is spared very strong in all cases. As a result of optimization, the MLC apertures are repetitively opening and closing and can be interpreted in an intuitive way. Applying the projection method for this knowledge-based VMAT delivery scheme for concave target volumes is an alternative technique for dose optimization. There are several properties, such as uniqueness of MLC motions and their continuous dependence on geometry and prescribed dose, that make this approach interesting to inverse planning. This method is still in an investigational stage, but promising results are presented. In future work it will be extended directly (without conceptual changes) in several directions to be more clinically applicable. Y1 - 2009 U6 - https://doi.org/10.1118/1.3173815 VL - 36 IS - 8 SP - 3764 EP - 3774 PB - American Association of Physicists in Medicine ER - TY - JOUR A1 - Dobler, Barbara A1 - Streck, Natalia A1 - Klein, Elisabeth A1 - Löschel, Rainer A1 - Haertl, Petra Maria A1 - Kölbl, Oliver T1 - Hybrid plan verification for intensity-modulated radiation therapy (IMRT) using the 2D ionization chamber array I'mRT MatriXX--a feasibility study JF - Physics in medicine and biology N2 - The 2D ionization chamber array I'mRT MatriXX (IBA, Schwarzenbruck, Germany) has been developed for absolute 2D dosimetry and verification of intensity-modulated radiation therapy (IMRT) for perpendicular beam incidence. The aim of this study is to evaluate the applicability of I'mRT MatriXX for oblique beam incidence and hybrid plan verification of IMRT with original gantry angles. For the assessment of angular dependence, open fields with gantry angles in steps of 10 degrees were calculated on a CT scan of I'mRT MatriXX. For hybrid plan verification, 17 clinical IMRT plans and one rotational plan were used. Calculations were performed with pencil beam (PB), collapsed cone (CC) and Monte Carlo (MC) methods, which had been previously validated. Measurements were conducted on an Elekta SynergyS linear accelerator. To assess the potential and limitations of the system, gamma evaluation was performed with different dose tolerances and distances to agreement. Hybrid plan verification passed the gamma test with 4% dose tolerance and 3 mm distance to agreement in all cases, in 82-88% of the cases for tolerances of 3%/3 mm, and in 59-76% of the cases if 3%/2 mm were used. Separate evaluation of the low dose and high dose regions showed that I'mRT MatriXX can be used for hybrid plan verification of IMRT plans within 3% dose tolerance and 3 mm distance to agreement with a relaxed dose tolerance of 4% in the low dose region outside the multileaf collimator (MLC). Y1 - 2010 U6 - https://doi.org/10.1088/0031-9155/55/2/N02 VL - 55 IS - 2 SP - N39 EP - N55 PB - IOP Publishing ER - TY - JOUR A1 - Hoegele, W. A1 - Löschel, Rainer A1 - Merkle, N. A1 - Zygmanski, Piotr T1 - An efficient inverse radiotherapy planning method for VMAT using quadratic programming optimization JF - Medical physics N2 - PURPOSE The purpose of this study is to investigate the feasibility of an inverse planning optimization approach for the Volumetric Modulated Arc Therapy (VMAT) based on quadratic programming and the projection method. The performance of this method is evaluated against a reference commercial planning system (eclipse(TM) for rapidarc(TM)) for clinically relevant cases. METHODS The inverse problem is posed in terms of a linear combination of basis functions representing arclet dose contributions and their respective linear coefficients as degrees of freedom. MLC motion is decomposed into basic motion patterns in an intuitive manner leading to a system of equations with a relatively small number of equations and unknowns. These equations are solved using quadratic programming under certain limiting physical conditions for the solution, such as the avoidance of negative dose during optimization and Monitor Unit reduction. The modeling by the projection method assures a unique treatment plan with beneficial properties, such as the explicit relation between organ weightings and the final dose distribution. Clinical cases studied include prostate and spine treatments. The optimized plans are evaluated by comparing isodose lines, DVH profiles for target and normal organs, and Monitor Units to those obtained by the clinical treatment planning system eclipse(TM). RESULTS The resulting dose distributions for a prostate (with rectum and bladder as organs at risk), and for a spine case (with kidneys, liver, lung and heart as organs at risk) are presented. Overall, the results indicate that similar plan qualities for quadratic programming (QP) and rapidarc(TM) could be achieved at significantly more efficient computational and planning effort using QP. Additionally, results for the quasimodo phantom [Bohsung et al., "IMRT treatment planning: A comparative inter-system and inter-centre planning exercise of the estro quasimodo group," Radiother. Oncol. 76(3), 354-361 (2005)] are presented as an example for an extreme concave case. CONCLUSION Quadratic programming is an alternative approach for inverse planning which generates clinically satisfying plans in comparison to the clinical system and constitutes an efficient optimization process characterized by uniqueness and reproducibility of the solution. Y1 - 2012 U6 - https://doi.org/10.1118/1.3671922 VL - 39 IS - 1 SP - 444 EP - 454 PB - American Association of Physicists in Medicine ER - TY - JOUR A1 - Schöpf, Nicolas A1 - Iseler, K. A1 - Sausele, I. T1 - Persistenz und Verschwinden. Pädagogische Organisationen im historischen Kontext JF - Zeitschrift für Soziologie der Erziehung und Sozialisation Y1 - 2007 SN - 1436-1957 VL - 27 IS - 4 SP - 442 EP - 447 PB - Beltz Juventa ER - TY - JOUR A1 - Zürner, Christian T1 - Religiöse Bildung in der säkularisierten Gesellschaft. Grundsatzüberlegungen mit Bezug auf den Philosophen Jürgen Habermas JF - Freies Christentum : auf der Suche nach neuen Wegen Y1 - 2007 SN - 0931-3834 VL - 59 IS - 3 SP - 67 EP - 69 ER - TY - JOUR A1 - Thieme, Dorothea A1 - Landenberger, M. T1 - Therapie der akuten tiefen Beinvenenthrombose - eine Literaturrecherche: Verbandtechniken im Vergleich JF - Pflegezeitschrift Y1 - 2009 VL - 62 IS - 4 SP - 206 EP - 209 ER - TY - JOUR A1 - Thieme, Dorothea A1 - Langer, G. A1 - Behrens, Johann T1 - Das Wissen Pflegender zur Kompressionstherapie - Studie zur Therapie der akuten tiefen Beinvenenthrombose JF - Pflegezeitschrift Y1 - 2009 VL - 62 IS - 5 SP - 296 EP - 301 ER -