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Radiation biology

the study of the effects of ionizing radiation on living tissue, to understand the harmful effects of x radiation

what happens when xrays are absorbed in patient tissue

chemical changes occur that result in biological damage

two mechanisms of radiation injury

ionization and free radical formation

ionization results from

when x-rays strike patient tissues

ionization is produced

through the photoelectric effect or compton scatter, results in formaiton of a positive atom and dislodged negative electron, interacts with other atoms in tissue

what happens when kinetic energy further ionizes

excitation occurs, breaking of molecular bonds, which cause chemical changes in cell result in biological damage

ionization may have little effect if chemical change do not alter

sensitive molecules, or such change may have profound effect on structure great importance to cell function DNA

free radical formation occurs

when an x-ray photon ionizes water, the primary component of living cells, water results in production of hydrogen and hydroxyl free radical, hydrogen peroxide

free radical

unchanged atom or molecule that exists with a single unpaired electron in its outermost shell, highly reactive and unstable

free radicals achieve stability by

recombining without causing change in the molecule, combine with other free radicals and cause changes, may combine with ordinary molecules to form a toxin(H2O2), capable producing widespread cellular changes

theories of radiation injury

direct and indirect

direct theory

cell damage results when ionizing radiation directly hits critical areas, or targets, within the cell. If photons directly strike dna, critical damage occurs

indirect theory

x-ray photons are absorbed within the cell and cause formation of toxin, which damage the cell, ex if absorbed by water in cell, free radicals turn it into peroxide, cause cellular dysfunction and biological damage

the theory of radiation injury that occurs most

is indirect theory because of high water content in cells

dose response curve

can be used to correlate the response or damage of tissue with the does or amount of radiation received,linear relationship indicates the tissue directly proportional to the dose

non threshold relationship

threshold does level for damage does not exist, no matter how small the amount of radiation received, some biologic damage occurs, no safe amount of radiation exposure

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