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Radiotherapy with heavy ion beam in the presence of platinum as a radiosensitizer Z. Habibi Kelishomi Email: Zhabibi@ibb.ut.ac.ir Introduction: Malignant tumors or cancers have now become one of the most frequent causes of death in human society; hence, new protocols have been developed with the purpose of focusing and maximizing the energy deposition of the ionizing particles into the volume of the tumor. Methods: First: Experiments consist of irradiation of dried DNA in vacuum with Ar ions at low keV energies for different time intervals. The DNA is analyzed by agarose gel electrophoresis. Second: DNA Plasmids (pBR322) loaded with different amounts of platinum contained in a terpyridine platinum chloride (PtTC) were irradiated by C6+ ions and Fe 26+ ions. The Linear Energy Transfer (LET) values ranged between 13.4 keV/µm and 550 keV/µm. In some experiments, dimethyl sulfoxide was added. Third: Chinese Hamster Ovary cells were incubated for six hours in medium containing 350 µM terpyridine platinum chloride, and then irradiated by fast ions C6+ and He2+, with Linear Energy Transfer within range 2–70 keV/µm. In some experiments, dimethyl sulfoxide was added to investigate the role of free radicals. The intracellular localization of platinum was determined by Nano Secondary Ion Mass Spectroscopy. Result: In all experiments, a significant increase in DNA strand breaks was observed when platinum was present. Also, experiments showed that for all LET examined, cell death rate is largely enhanced when irradiating in presence of PtTC. They indicate that molecules containing high-Z elements might act as sensitize. Discussion and conclusion: These findings show that more DNA breaks are induced by atomic ions when platinum is present, and hadrontherapy or protontherapy therapeutic index could be improved by combining irradiation procedure with concomitant chemotherapy protocols using platinum salts. Keywords: Hadrontherapy, Auger effect, Cancer therapy, radiosensitizing, platinum compounds. References  K. Kobayashi, N. Usami, E. Porcel, S. Lacombe, C. Le Sech, Enhancement of radiation effect by heavy elements, Mutation Research. 704 (2010) 123–131.  S. Lacombe, C. Le Sech, Advances in radiation biology: radiosensitization in DNA and living cells, Surf. Sci. 603 (2009) 1953–1960.
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