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  • Author: Ryszard Dąbrowski x
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Testing of a sag of a dosimetry system rotating with a gantry using the interplay effect between detector motion and MLC motion

Abstract

Purpose: An interplay between detector motion and MLC motion is a source of measurement error, when dose for dynamic arc is measured using a dosimetry system moving relative to the beam central axis during its rotation with a gantry. The purpose of this study is to develop and to evaluate a method of quantitative testing of a sag/flex of such dosimetry systems. Methods: The method is based on evaluation of relative differences between signals measured for two single arc beams, where a narrow slit field is sliding during gantry movement in opposite directions. The component of a measurement error related to the interplay effect was first assessed based on theoretical computer simulations and then on measurements for four dosimetry systems. The sag pattern of EPID and 2D array was extracted from the measurement results. Results: The simulations showed a 4 mm difference in field width and 3.3% difference in relative signals at beam axis between test beams where the slit field swept over 19 cm in opposite directions ( sinusoidal sag pattern with amplitude of 1 mm was assumed). The signal differences exceeding 4% and 5% were measured for EPID and 2D array, respectively. Conclusions: Even relatively small detector sag (less than 1 mm) can produce significant measurement error; therefore, the detector sag test should be an obligatory component of a validation of rotating dosimetry systems used for QA of dynamic arcs.

Open access
INFLUENCE OF SALIVA AND ITS SUBSTITUTES ON CORROSION OF SOME IMPLANT ALLOYS

Abstract

The purpose of this paper is evaluation of the influence of human saliva and its substitutes on the corrosion resistance of some implant alloys used in stomatology, which included: austenitic steel (316L), titanium alloy (Ti6Al4V), and cobalt alloy (CoCrMo). Corrosion studies were conducted by means of the potentiodynamic method with the application of the VoltaLab 21 kit with VoltaMaster 4 software. The reference electrode was a saturated calomel electrode (SCE), whereas the counter electrode was a platinum electrode. The results of conducted studies indicate an increased current density in the passive range on potentiodynamic curves of studied alloys in the environment of human saliva, and also in a commercial saliva solution - Mucinox. On the basis of conducted corrosion studies, it can be stated that in terms of corrosion resistance the developed saliva substitutes may constitute competitive solutions to commercial saliva substitutes. The prepared substitutes should be studied further from the perspective of practical application for patients. The original value of the paper is a proposition of new saliva substitutes.

Open access