58 Porównanie zamierzonych współczynników TAR i SAR dla źródła 60Co – Theratron 780 z danymi literaturowymi

WprowadzenieWspółczynnik TAR i SAR pozwalają na obliczenie dawek dla pól nieregularnych lub zawierających osłony poprzez podzielenie ich na wiele pól i policzenie wkładu do całkowitej dawki.MetodaPomiarów na Theratronie 780E dokonano za pomocą fantomu wodnego PTW z oprogramowaniem Mephysto. Pomiary rozpoczęto od najmniejszego pola 5×5 cm i od powierzchni wody. Komora jonizacyjna typu 2271 (0,6 mm) była połączona z dawkomierzem firmy Nuclear Enterprise. Pomiary w wodzie zakończono na największym polu 35×35 cm. Głębokość maksymalna 30 cm. Następnie dokonano w tych samych warunkach pomiarów w powietrzu. Zachowano tę samą geometrię pomiarów. Pomiarów dokonano z nasadką build up, aby zachować równowagę elektronową.WynikiZamierzone współczynniki TAR i SAR dla źródła 60Co porównano z danymi literaturowymi. Dla małych pól, do 10 cm i na głębokości 0,5 cm uzyskano zgodność w granicach 1%. Dla pól większych różnice wzrosły do 3%. Wraz ze wzrostem głębokości pomiaru zgodność malała. Przy dużych głębokościach, powyżej 15 cm rozbieżności w wynikach osiągnęły 40°f. Uzyskane dawki dla tej samej głębokości i pól od pola zerowego do pola 35×35 cm zachowują charakterystykę zgodną z danymi literaturowymi.WnioskiWykonane pomiary były zgodne z literaturowymi. Krzywe opisujące zależność TAR i SAR od wielkości pola, osiągają dla dużych pól charakterystyczne plateau. Z analizy wyników wynika, że coraz bardziej uwidaczniają się różnice dla większych głębokości. Okazało się, że zbliżając się z komorą jonizacyjną do dna fantomu, coraz więcej promieniowania rozproszonego od jego dna i stołu terapeutycznego docierało do dozymetru. Dane literaturowe nie uwzględniają tych przyczynków. Promieniowanie pochodzące od stołu powinno być uwzględnione, gdyż w praktyce medycznej pacjent leży na stole terapeutycznym

59. Verification of the 3-D dose calculation algorithm during total skin electron irradiation with the rotary-dual field technique

Total skin electron irradiation is the commonly used procedure in the treatment of mycosis fungoides. The aim of this paper was to verify the elaborated algorithm for dose calculation during total skin electron irradiation with rotary-dual fields technique (TSEI-RD).Material and method: Authors modified the 2-D algorithm published by Podgorsak taking account of dose distribution along the body midline and doses in the body on a larger depth than in the skin. Depth-dose function, beam profile were measured in TSEI-RD conditions (spoiler, source-skin distance SSD=350cm, field size: 36×36cm at 100cm). Cylindrical vax phantom was used to calculate and then to measure the doses in a depth of 0.4cm during exposure to the electron beam of 6 MeV (at the output of Clinac-2300CD accelerator). Phantom was rotating with the pre-calculated speed during constant exposure to two fields executed one by one in each fraction. Thermoluminescent detectors (TLD) were used for in-phantom dose measurements and Marcus ionization chamber was used for calibration of TLD. Dose homogeneity on the phantom surface was checked for three phantoms with different diameters of 20, 30 and 40cm. Phantoms were irradiated at different rotating speeds.Initial results: Doses measured by TLD were on average by 4% lower than doses pre-calculated using the modified algorithm. Mean doses normalized to those pre-calculated and their standard deviations (both in per cents) were respectively: 96.1% and 0.4% for phantom with diameter of 20; 96.5% and 0.7% for diameter of 30cm and 96.0% and 0.8% for diameter of 40cm.Conclusions: Measured doses proved correctness of elaborated algorithm. Very low standard deviations are resulting from regular cylindrical shape of the phantoms

Properties of neutron doped multicrystalline silicon for solar cells

The technology of neutron transmutation doping of silicon wafers in MARIA nuclear research reactor is described. The studies of the radiation defects performed with positron annihilation confirmed that divacancies dominate in the irradiated material. Thermal treatment of irradiated silicon at 700-1000°C produces void - phosphorus complexes and void aggregates. The resistivity of the samples produced by neutron transmutation doping was found to be uniform within 2.5% limits. The severe reduction of the minority carrier lifetime in irradiated samples was confirmed

39. Pulsed dose rate brachytherapy – describing of a method and a review of clinical applications

IntroductionPulsed Dose Rate (PDR) treatment is a new brachytherapy modality that combines physical adventages of high-dose-rate (HDR) technology (isodose optimization, radiation safety) with the radiobiological adventages of low-dose-rate (LDR) brachytherapy.Pulsed brachytherapy consists of using a stronger radiation source than for LDR brachytherapy and is giving a senes of short exposures of 10 to 30 minutes in every hour to approximately the same total dose in the same overall as with the LDR. Modern afterloading equipment offers some advantages over intersitial or intracavitary insertion of separate needles, tubes, seeds or wires. Isodose volumes in tissue can be created flexibly by a combination of careful placement of the catheter and adjustment of the dwell times of the computerized stepping source. Automatic removal of the radiation sources into a shielded safe eliminates radiation exposures to staff and visitors. Radiation exposure is also eliminated to the staff who formerly loaded and unloaded a multiplicity of radioactive sources into the catheters, ovoids, tubes etc.Material and methodsThis retrospective study based on summarized clinical investigations analyses the feasibility, differences between methods of brachytherapy and preliminary oncologic results of PDR brachytherapy.Since July 2000 15 patients were treated in Greatpoland Cancer Center using PDR brachytherapy. They were 10 patients with recurrent brain malignant glioma, 2 with recurrent nasopharyngeal cancer, and patients with lip cancer, recurrent breast cancer and recurrent salivary gland cancer. Only patient with lip cancer was treated radically. Nucletron PDR unit with 1 Ci source and PLATO planning system were used.ResultsShort time of observation doesn’t allow to draw a radical conclusions. On the ground of literature and preliminary own results it seems that PDR brachytherapy is save and efficient method of treatment. The most important complication was a local infection in place of implanted catheter. In some cases (for example in patients with recurrent malignant glioma after teletherapy) PDR brachytherapy perhaps could be a treatment of choice

Clay mineralogy, strontium and neodymium isotope ratios in the sediments of two High Arctic catchments (Svalbard)

he identification of sediment sources to the ocean is a prerequisite to using marine sediment cores to extract information on past climate and ocean circulation. Sr and Nd isotopes are classical tools with which to trace source provenance. Despite considerable interest in the Arctic Ocean, the circum-Arctic source regions are poorly characterised in terms of their Sr and Nd isotopic compositions. In this study we present Sr and Nd isotope data from the Paleogene Central Basin sediments of Svalbard, including the first published data of stream suspended sediments from Svalbard. The stream suspended sediments exhibit considerable isotopic variation (εNd = −20.6 to −13.4; 87Sr ∕ 86Sr = 0.73421 to 0.74704) which can be related to the depositional history of the sedimentary formations from which they are derived. In combination with analysis of the clay mineralogy of catchment rocks and sediments, we suggest that the Central Basin sedimentary rocks were derived from two sources. One source is Proterozoic sediments derived from Greenlandic basement rocks which are rich in illite and have high 87Sr ∕ 86Sr and low εNd values. The second source is Carboniferous to Jurassic sediments derived from Siberian basalts which are rich in smectite and have low 87Sr ∕ 86Sr and high εNd values. Due to a change in depositional conditions throughout the Paleogene (from deep sea to continental) the relative proportions of these two sources vary in the Central Basin formations. The modern stream suspended sediment isotopic composition is then controlled by modern processes, in particular glaciation, which determines the present-day exposure of the formations and therefore the relative contribution of each formation to the stream suspended sediment load. This study demonstrates that the Nd isotopic composition of stream suspended sediments exhibits seasonal variation, which likely mirrors longer-term hydrological changes, with implications for source provenance studies based on fixed end-members through time

An Analysis of the Quantum Penny Flip Game using Geometric Algebra

We analyze the quantum penny flip game using geometric algebra and so determine all possible unitary transformations which enable the player Q to implement a winning strategy. Geometric algebra provides a clear visual picture of the quantum game and its strategies, as well as providing a simple and direct derivation of the winning transformation, which we demonstrate can be parametrized by two angles. For comparison we derive the same general winning strategy by conventional means using density matrices.Comment: 8 Pages, 1 Figure, accepted for publication in the Journal of Physical Society of Japa