Use of different CT scanning protocols leads to variations of up to 20% in the HU values. This can result in a mean systematic dose error of 1.5%. Specific conversion tables and automatic CT scanning protocol recognition could reduce dose errors of these types.
The assessment of the exposure to cosmic radiation onboard aircraft is one of the preoccupations of bodies responsible for radiation protection. Cosmic particle flux is significantly higher onboard aircraft than at ground level and its intensity depends on the solar activity. The dose is usually estimated using codes validated by the experimental data. In this paper, a comparison of various codes is presented, some of them are used routinely, to assess the dose received by the aircraft crew caused by the galactic cosmic radiation. Results are provided for periods close to solar maximum and minimum and for selected flights covering major commercial routes in the world. The overall agreement between the codes, particularly for those routinely used for aircraft crew dosimetry, was better than + + + + +20 % from the median in all but two cases. The agreement within the codes is considered to be fully satisfactory for radiation protection purposes.
Positron lifetime measurements are performed in branched polyethylene in the temperature range between −195 and +40 °C. The lifetime spectra are resolved into four components, and corresponding annihilation mechanisms are discussed. Within the temperature range mentioned above four different transitions at −145, −95, −58, and −13 °C can be observed. From the behaviour of the lifetime parameters of the longest‐lived component it is possible to deduce a criterion for the glass transition, which is situated at −13 °C. Additionally, time effects of the lifetime parameters are detected.
A system for dosimetric verification of intensity-modulated radiotherapy (IMRT) treatment plans using absolute calibrated radiographic films is presented. At our institution this verification procedure is performed for all IMRT treatment plans prior to patient irradiation. Therefore clinical treatment plans are transferred to a phantom and recalculated. Composite treatment plans are irradiated to a single film. Film density to absolute dose conversion is performed automatically based on a single calibration film. A software application encompassing film calibration, 2D registration of measurement and calculated distributions, image fusion, and a number of visual and quantitative evaluation utilities was developed. The main topic of this paper is a performance analysis for this quality assurance procedure, with regard to the specification of tolerance levels for quantitative evaluations. Spatial and dosimetric precision and accuracy were determined for the entire procedure, comprising all possible sources of error. The overall dosimetric and spatial measurement uncertainties obtained thereby were 1.9% and 0.8 mm respectively. Based on these results, we specified 5% dose difference and 3 mm distance-to-agreement as our tolerance levels for patient-specific quality assurance for IMRT treatments.
The acceptance and usability of personal protection against solar UV radiation was evaluated in a field study with a group of tinsmiths in Austria. The personal protective measures (PPM) tested involved four categories: shirts, headwear, sunglasses and topically applied sunscreens; at least six different products per category were tested. Recommendations for the "ideal" shirt, headwear, pair of sunglasses and topical sunscreen are given based on data from questionnaires, i.e., from the point of view of the workers, independently from the actual physical level of protection (such as low transmittance or area of coverage) provided. It is argued that in practice it is important to consider the acceptance and usability of protective measures as well as the level of physical protection when providing PPM.
Positron lifetime spectra in γ‐irradiated teflon are measured in the dose range up to 20 Mrad and clearly resolved into four lifetime components without any constraints. With increasing dose, the longest and the second‐longest lifetime decrease slightly, whereas the two shortest lifetimes remain constant. The intensity of the second‐shortest component increases very much on the expense of the other intensities, especially of that of the longest‐lived component. The identification of the four lifetime components with corresponding annihilation mechanisms is discussed.
Positron lifetime measurements on linear polyethylene are performed in the temperature range between -192 and + 180 "C. The results are compared with works on branched polyethylene. The criterion for the glass transition given earlier is proved. Branched and linear polyethylene show the same transitions at approximately the same temperatures. The only exception is the transition at -58 "C found in branched polyethylene only. Most deviations between the results of the two polyethylene samples can be explained by the different number of branching points or different cristallinity. Time effects of the lifetime parameters below the glass transition are observed.
Positronen-Lebensdauermessungen in linearemPolyathylen werden im Temperaturbereich von -192 bis + 180 "C durchgefiihrt. Die Resultate werden mit Untersuchungen an verzweigtem Polyathylen verglichen. Ein friiher fiir den Glasiibergang abgeleitetes Kriterium bestatigt sich. Verzweigtes und lineares Polyathylen zeigen dieselben Ubergange bei etwa denselben Temperaturen. Die einzige Ausnahme bildet der obergang bei -58 "C, der nur beim verzweigten Polyathylen nachweisbar ist. Die meisten Abweichungen zwischen den Resultaten beider Polyathylenproben konnen auf die verschiedene Anzahl der Verzweigungspunkte und unterschiedliche Kristallinitat zuriickgefiihrt werden. Unter dem Glasiibergang werden zeitliche Effekte der Lebensdauerparameter beobachtet.
Our aim in this study was to distinguish quantitatively between the localization accuracy of a commercially available stereotactic fixation device as claimed by the manufacturer and the target accuracy as measured by a user, applying neuroradiologic imaging in Gamma Knife planning and phantom irradiation. Missing the target is the most serious possible failure in Gamma Knife and Linac therapy. To reduce this risk, we developed a quality control algorithm and designed a phantom. To evaluate the accuracy of the targeting procedure with a Leksell Gamma unit, and to experience the possible errors in all procedural steps, irradiations of phantoms were performed, using the so-called "unknown" targeting method. Accuracy is defined by the extent of spatial deviation of the irradiated target from the calculated target. Digital imaging was used for therapy planning. GafChromic films, which had been irradiated while affixed to a specially developed phantom, were used for measuring the precision of the radiation unit. A series of MR images (in two plains: transverse and coronal) was acquired sequentially to image the three-dimensional (3-D) volume of the phantom. The results obtained for isocentric accuracy of the Leksell Gamma unit, model B, were in good agreement to the calculated position. The observed spatial deviations between calculated and irradiated targets is less than 1 mm. The newly designed phantom and quality control algorithm are useful in quality assurance measurements of stereotactic radiation therapy.
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