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Optical system for precise isocenter measurement

Kukołowicz Paweł, Szalkowski Dariusz, Jackowska-Zduniak Beata, Tarchalski Mikołaj

Polish Journal of Medical Physics and Engineering

2023

Vol. 29, Iss. 4

178--184

Introduction: The geometrical precision of the machines is essential for effective and safe radiotherapy. Methods currently used for the measurement of the mechanical isocenter have many limitations. In this work, the optical system NaviRation for very precise measurement of mechanical accelerator isocenter is described. The results of the measurement of the isocenter for linear accelerator are also presented. Materials and methods: An optical system for measuring the accelerator isocenter was designed and built. The optical system consists of two cameras recording the target position made according to a patented Zeiss technology. About 1,200 pairs of images are recorded during the rotation of the gantry, collimator and treatment table. Mathematical analysis of these images makes it possible to determine the location of the target center during rotation. In order to verify the accuracy of the measurements, a device simulating rotational motion was designed. The measurement results were also verified at the Central Office of Measures. The system must be calibrated each time before taking measurements. In this article, we present the results of measurements for the Versa HD accelerator. Results: The accuracy of determining the current position of the axis of rotation was 0.15 mm. The time of taking measurements of all rotations does not exceed 20 minutes. Measurement results for the Versa HD accelerator showed that this accelerator met the criteria described by TG142 of the AAPM. The diameter of the gantry, collimator and table isocenter spheres were 1.5 mm, 0.3 mm and 0.4 mm, respectively. Conclusions: The system enables precise, fast and simple mechanical isocenter measurement of the gantry, collimator and treatment table. It is also possible to perform all tests related to the measurements of distances, e.g. quality control of distance indicator, and distance of the table movement. The isocenter is measured independently of the accelerator for which measurements are made.

Stochastic models of the slow/fast type of atrioventricular nodal reentrant tachycardia and tachycardia with conduction aberration

Jackowska-Zduniak Beata

International Journal of Applied Mathematics and Computer Science

2022

Vol. 32, no. 3

429--440

Models are proposed to describe the heart’s action potential. A system of stochastic differential equations is used to recreate pathological behaviour in the heart such as atrioventricular nodal reentrant tachycardia (AVNRT) and also AVNRT with conduction aberration. Part of the population has abnormal accessory pathways: fast and slow. An additional pathway is not always induced, since the deterministic model is not proper due to a stochasticity in this process. Introduction of a stochastic term allows modelling a pre-excitation perturbation (such as unexpected excitation by premature contractions in atrium (PAC)) which triggers the mechanism of AVNRT. Also, a system of AVNRT with additional conduction aberration, which is a rare type of arrhythmia, is considered. The aim of this work is to propose a mathematical model superior to the deterministic one that recreates this disease better and allows understanding its mechanism and physical dependencies, which may help to propose a new therapy of AVNRT. Results are illustrated with numerical solutions.