Dommages induits par les électrons secondaires et les rayons X
Abstract
X-rays are widely used in medical diagnosis and radiotherapy. The effects of X-rays on cells are dominated by their actions on the cellular DNA. The interaction of X-rays with DNA produces photoelectrons, Auger electrons, Compton electrons and large quantities of secondary electrons (SE), the majority of which have energies lower than 70 eV. This thesis aims to compare the DNA damage induced by SE and X-rays. A dosimetry method to measure the absorbed dose of Al[subscript k alpha] X-rays (1.5 keV) in ultrahigh vacuum chamber (UHV) using radiochromatic dosimetry films and a color scanner was developed. This provided the value for the absorbed dose in dry biological samples irradiated under UHV, allowing direct comparison of DNA damage induced by Al[subscript k alpha] X-rays and SE. The induction of covalent interduplex DNA crosslinks (CL) by X-rays was detected using restriction enzyme digestion and alkaline agarose gel electrophoresis. The G value for CL induction in DNA in UHV by Al[subscript k alpha] X-rays is 16 « 4 nmol J[superscript -1], 2.8 fold that of double strand breaks (DSB). G(CL) in air by soft X-rays (14.8 keV) is 3 « 1([gamma] [approximate] 6, [gamma] is defined as the number of water molecules per nucleotide,) and 3.2 « 0.4 ([gamma] [approximate] 21) nmol J[superscript -1], 61 and 89% of those for DSB. These results suggest that CL is an important type of DNA damage, possibly as important as DSB in radiobiology. A new method of studying SE-induced DNA damage…
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