radiology biology

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