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S2
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5è. seminari internacional sobre imatge mèdica i les tecnologies de la informació
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Aplicacions biomèdiques de la radiació de sincrotó: aplicacions en teràpia
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Geraldine Le Duc, responsable de l'activitat biomèdica de l'estació ID17 ESRF, Grenoble
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Using a synchrotron source as a tool for radiothearpy : the example of the ESRF.
Gliomas are among the most frequent primary brain tumors in adults, with an incidence of approximately (5-11)/105 in industrial countries. The treatment of high-grade gliomas is palliative rather than curative, despite a combination of surgery, chemotherapy and radiotherapy. Gliomas are extremely radioresistant, while surrounding normal tissues remain radiosensitive especially in infants.
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At the ESRF, two innovative radiotherapy techniques, namely the Microbeam Radiation Therapy (MRT) and the Stereotactic Synchrotron Radiation Therapy (SSRT) are under development. MRT differs from other radiotherapy techniques in the use of array of spatially fractionated X-ray beams (typically few microns wide and some hundreds of microns spaced); in this way high doses (several hundreds of grays in a single fraction, delivered in microbeams) is tolerated by healthy tissues. This technique can be applied only at SR sources because MRT needs highly intense (allowing subsecond irradiations in order to prevent motion artifacts of the subject), highly energetic (allowing a deep penetration in tissue) X-ray beams of negligible divergence (allowing the production of a sharply defined dose gradient in tissues).
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The SSRT technique is based on insertion of a substance containing a high Z element into the tumour, and on the irradiation of the target with monochromatic X-rays at energies above the K-edge of the element; this produces a local dose enhancement. One possible explanation of this effect involves the release a cascade of Auger electrons following photoelectric absorption in the incorporated heavy element. SSRT, performed in CT mode, to deposit only a fraction of the delivered doses in the tissues surrounding the tumour, was applied to rats bearing gliomas using iodine as a high Z material or the chemotherapic drug cisplatinum CDDP (i.e. to profit from both the dose enhancement and the chemotherapic effect). The future radiotherapy projects at ID17 are twofold. Preclinical trials are concentrated on the optimization of ballistic and dose delivery, and on the selection of the optimal drug for the local dose enhancement. An history of results, as well as recent results and still unanswered questions will be presented during this talk. Protocols for clinical trials in SSRT are presently under advanced stage of preparation. In parallel, the white beam hutch for MRT is under full refurbishment to permit a refinement of irradiation protocols in optimal experimental conditions, with the final aim of reaching the clinical application.
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