397 research outputs found
Moving Phantom Study of Stereotactic Body Radiation Therapy for Lung Cancer
No full textTo assess the accuracy of current stereotactic body radiation therapy (SBRT) lung treatment methodologies, we performed a systematic evaluation using phantoms that simulated motions from real patients (irregular motions) as well as sinusoidal motions (regular motions). The irregular patterns investigated in this study were of two types: small range irregular breathing motions (=10mm) and large range irregular breathing motions (=20mm). Four-dimensional computed tomography (4DCT) and cone beam computed tomography (CBCT) are important methodologies for SBRT, but previously have only been used to evaluate regular patterns. For targets moving regularly or irregularly within a small range (7.0 ± 1.8 mm, n = 6), we observed good agreement between the measured and computed dose distributions. However, for targets moving irregularly with a larger range (20.8 ± 2.6 mm, n = 4), the measured isodose lines were found to be shifted relative to the planned distribution, resulting in an underdosing (over 20%) in a portion of the PTV. In this underdosed volume, 1-2% of the PTV is underdosed by over 18 Gy, causing a 35-40% drop in the local control rate. We further observed that the discrepancy between the planned and measured dose distribution was due to the inaccurate representation of the irregular target motion in the maximum intensity projection (MIP) images generated from 4DCT, which could not be corrected by CBCT. A method of Extended Distance Virtual Isocenter (EDVI) was developed to lower the toxicity of healthy tissues. In all, caution should be used when planning from 4DCT images in the presence of large and irregular target motion. The inaccuracy inherent in 4DCT MIP and CBCT images can be mitigated through the application of methodologies to reduce respiratory motion, such as abdominal compression, and through the use of volumetric image guidance to assure precise targeting with minimal shifts
An evaluation of very high energy electron beams (up to 250 MeV) in radiation therapy
No full textThe purpose of this study was to evaluate very high energy electron beams in radiation therapy. Radiation therapy for cancer treatment has evolved towards increased radiation dose conformality on a targeted volume. Although heavy charged particles potentially provide the most conformal therapy, photon beams are more common due to cost. A recent innovation in photon beam treatment is the use of dynamic multileaf collimation to produce small beams which are effectively scanned within a treatment field. This technique is cumbersome relying upon moving mechanical parts rendering the procedure time consuming, compared with beams which may be electromagnetically scanned. Electrons may be electromagnetically scanned. Clinically available electron energies, less than 50 MeV, have limitations with regard to penetration depth, penumbra and large angle scattering. Monte Carlo simulations with the PENELOPE code were performed to evaluate very high energy electrons, up to 250 MeV and it was found that the limitations of clinically available electron energies were overcome. Very high energy electrons were found to be adequately penetrating to treat deep seated targets, with penumbra comparable to photons. Large angle scattering which occur as the electron approaches the end of its range is irrelevant clinically with very high energy electrons as the range of these beams extends beyond the patient volume. Additionally, it was found that very high energy electrons do not exhibit loss of electronic equilibrium in low density media as do conventional photons equating to improved dose distributions predicted for site specific targets. The applicability of normal tissue complication probability and tumor control probability were evaluated for both very high energy electrons and photons. Treatment unit design was evaluated based on electron accelerator designs. The scanning magnet strength required for the proposed accelerator was calculated to be approximately 1.0 Tesla. Secondary radiation production from neutrons produced in tissue and induced radioactivity thereof was estimated to increase dose by less than three percent. Based on these investigations, very high energy electrons have potential application in radiation therapy as they can provide very fine intensity modulated treatment with promising advantages for targets in low density regions, such as the lung
Evaluation of dose distribution for targets near inhomogeneities in photon beam radiation therapy
No full textPurpose. The purpose of this work was to evaluate the accuracy of the dose calculated in the presence of inhomogeneities by the top performing algorithms employed by some commercially available modern treatment planning systems for the external photon beam radiotherapy. Materials and methods. A new Fluence Map Monte Carlo (FMMC) method that can serve as a benchmark for such evaluation under certain conditions for a given linear accelerator was developed and tested. Dose perturbation on the inhomogeneities composed of high, low and very low density materials was measured with film dosimeters and calculated with various algorithms. The algorithms included general purpose Monte Carlo and FMMC methods as well as the treatment planning dose calculation algorithms such as pencil beam kernel convolution, point kernel convolution, and superposition, which is the most accurate of the three. Results. The dosimetric comparison results for high density materials obtained by FMMC, superposition, and measurement revealed that the superposition overestimates (up to 16%) of the dose downstream of the inhomogeneity. A very low density medium such as an air cavity was found to have an overestimation (up to 20%) of the dose by the superposition algorithm. The dose in a lung (low density medium) equivalent material was found to be significantly overestimated when calculated with either point kernel (up to 20%) or pencil beam kernel (up to 40%) convolution algorithms. Conclusion. Based on these findings it is recommended that a particular attention should be given to the verification of a dose calculated for the treatment of tumors located in anatomical sites where inhomogeneities are predominant. In many cases a verification process can be successfully performed with the proposed FMMC method which is shown to have a good match with the measurements
In memory of Professor Lech Wojtczak, researcher and person
No full textProfessor Lech Wojtczak spent his entire scientific life at the Nencki Institute of Experimental Biology PAS, where he worked since 1947. He is the author or co-author of two hundred scientific papers, promoted 15 doctors of science, was the Full Member of PAS and has been awarded with several prizes and honors. Among his students are three successive directors of the Nencki Institute, the authors of the present article. Scientific interests of Professor Lech Wojtczak were always dealing with bioenergectics, a discipline that he led in Poland and Eastern-Central Europe. In particular, his studies focused on the role of fatty acids and their derivatives on bioenergetics, on the regulatory role of surface potential of biomembranes on enzymatic and transport activities, on the regulatory role of calcium and magnesium in mitochondria, on the role of free oxigen radicals in bioenergetics, etc. Apart from being a great scientist, Lech Wojtczak was also a fantastic teacher, and an excellent scientific supervisor. Being well recognized in the world, he was placing members of his research group in foreign laboratories, as well as was sending tchem to courses and conferences. This was opening their minds to the world, and to other cultures, and allowed Lech Wojtczak to form from his collaborators the next generation of good scientists and future leaders. The list of the most important pupils of Professor Wojtczak is given in the article. Lech was also excellent in social contacts, and in creating a friendly atmosphere. Together with his wife Anna, they kept an open home, often inviting collaborators to parties that usually led to long scientific discussions. With the sudden death of Pofessor Lech Wojtczak Polish science suffered a great loss. This eminent researcher, the father of Polish bioenergetics, but also a warm and modest person, will be dearly missed
A REVIEW OF THE BOOK: PATRYK WAWRZYŃSKI, PREZYDENT LECH KACZYŃSKI. NARRACJE NIEDOKOŃCZONE [PRESIDENT LECH KACZYNSKI. THE UNFINISHED NARRATIVES], WYDAWNICTWO ADAM MARSZAŁEK, TORUŃ 2012
No full textWith these words of Mark Antony – as a motto – Patrick Wawrzyński could start his book. Published in 2012, the work is titled "President Lech Kaczynski. The unfinished narratives" (Prezydent Lech Kaczyński. Narracje niedokończone), and it is just such an attempt of doing justice to the tragically deceased president of the Republic of Poland. The author has undertaken the task of presenting the views of Lech Kaczynski as they actually were – separating them from incorrect interpretations and opinions attributed by other actors of the Polish political scene: his opponents as well as allies
In one breath (Jednym tchem) performed at the Theatre of the Eighth Day
Get PDFThis text deals with the 1971 play Jednym tchem (In one breath), performed at the Theatre of the Eighth Day (Teatr Ósmego Dnia) and based on Stanisław Barańczak’s poem. Lech Raczak outlines the methods used in the play, the characters, way of presenting a poetic text and the music in the performance. The author uses fragments of performance records published in his previous book Szaleństwo i metoda. 48 tekstów o teatrze (Madness and method. 48 texts about theatre) (Wydawnictwo Miejskie Posnania, Poznań 2012).<br /
Lech Ratajski
No full textLech Ratajski was born on 26 April 1921, in Rawa Mazowiecka, in a teachers' family. In 1939 he obtained the school-leaving certificate in Łomża. During the II World War he worked as a teacher and a clerk. He was also a member of the Home Army (AK) and he took part in the sabotage actions for which in 1949 he was honoured with the Cross of Valour. After the war he studied at the Academy of Fine Arts in Cracow for two years. In 1950 he graduated of the Jagiellonian University in Cracow with a degree in geography. As a student he collaborated with the popular monthly magazine „Poznaj Świat” (Know the World) for which he elaborated maps, designed covers, and wrote short notes. In 1950, accordingly to his interests, he took a post at the Department of Regional Geography within the Geographical Institute of the University of Warsaw. He wrote on the subject of the geographic names and in 1959 he was a co-author of the extensive specification comprising 20,000 geographical names. He was also the co-author of the wall economic charts of Poland and of the world, that were innovative in the Polish cartography of those days. He continuously collaborated with the magazine „Poznaj Świat” that was being published in Warsaw since the end of 1955 and he was its Editor-in-chief since 1968. He was the author of many articles and notes on the regional geography and of a book - a compendium of knowledge on Africa. The main field of his scientific interest was the thematic cartography, especially the economic maps and to this issue both his dissertations were related: the doctor's dissertation (1962) on the achievements of the Polish economic cartography in 20th century and the habilitation dissertation ( 1966) on industrial maps and their cartometric value. He devised the model of the cartographic methods of presentation, the model of cartographic generalisation, and the proposition of economic maps signs standardisation. Since 1968 he was the chairman of the Working Group and later of the Commission on Communication in Cartography at the International Cartographical Association (ICA). In the academic year 1971/1972 he lectured at the University of Edmonton and participated in the International Cartographical Association conference in Ottawa, at which he was elected the Vice-president of the Association. During his stay in Canada he prepared the textbook Methodology of the socioeconomic cartography that was published in 1973, and its second, updated edition was published in 1989. At the end of 1967 he was appointed the professorship at the Chair of Cartography where he introduced many didactic innovations - among others the free-hand drawing. In 1973 he employed dr W. Grygorenko (the future Chairman of the Chair) to teach computer cartography to the students. He tutored approximately 90 master's thesis, including 17 on the economic charts of the Polish voivodeships. In 1973- 1977 four employees of his Chair were promoted doctors. In 1973 Lech Ratajski obtained the title of a professor. He served several functions at the Polish Geographic Society, among others he was the President of the Commission of Cartography. In 1976 he was honoured with the medal of the Society. His bibliography comprises over 400 items including over 150 on cartography. He was the author of 30 portable and wall maps and approx. 600 annex maps to articles, books, and encyclopedias. Lech Ratajski died on 22 November 1977, in Warsaw
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