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Quel niveau de qualité de traitement peut être obtenu par un système d'irradiation robotisé guidé par l'image en radiothérapie (CyberKnifeTM)

Abstract : The CyberKnifeTM consists of 6MV LINAC mounted on a robotic arm, with six degree of freedom and is coupled to an image guiding system, allowing us to guide the irradiation beams toward the target. The aim is to improve the treatment accuracy and to reduce the irradiation of critical surrounding organs. The treatment is realized by the isotropic convergence of hundreds of orientations for creating up to 1200 mini-beams, which are orientated to the target with submillimetric accuracy. This group is completed by a treatment couch, which is also mounted on a robotized arm, that offers 6 additional degrees of freedom, allowing an additional improvement of accuracy, and eliminates the possible limitations. Using its subsystem SynchronyTM, the CyberKnifeTM is capable of treating the abdo -thoracic tumors, which move with respiration, by moving dynamically the LINAC to compensate the respiratory motion of the tumors. The high dose level, which is used in this kind of hypofractionated treatment, makes the smallest error unacceptable, and needs a very high geometric accuracy with keeping a maximal dosimetric accuracy. Our work is dedicated to evaluate the quality of treatment, in the terms of dosimetric and geometric accuracies. For the different modes of tracking, which are available in the system in static mode, and dynamic mode with respiratory motion tracking. By using different kinds of detectors (ionization chambers, radiochromic films) and three different platforms, which allow simulating simple respiratory motion, real respiratory motion coming from real treated patients, and finally complex motion with hysteresis. The results show clearly the high dosimetric accuracy of the system; this is accompanied by a submillimetric geometric accuracy. This geometric accuracy degrades slightly, when treating in dynamic mode with respiratory tracking by SynchronyTM, and especially when the respiratory cycles show a high variation in amplitudes, while the dosimetric accuracy is maintained. The presence of hysteresis causes a degradation of geometric accuracy, in comparison with the measured one for linear respiratory motion. The use of gamma index has proved à high matching level between the prescribed and delivered dose distributions. Briefly, the CyberKnifeTM meets the performances claimed by the manufacturer, and is reliable and capable of realizing a high quality radiosurgery.
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Submitted on : Monday, November 7, 2011 - 11:24:48 AM
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Safa Al Khawaja. Quel niveau de qualité de traitement peut être obtenu par un système d'irradiation robotisé guidé par l'image en radiothérapie (CyberKnifeTM). Sciences du Vivant [q-bio]. Institut National Polytechnique de Lorraine - INPL, 2011. Français. ⟨tel-00638737⟩

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