Dose fractionation  From Wikipedia, the free encyclopedia Jump
to: navigation, search  Experiments in radiation biology have
found that as the absorbed dose of radiation increases, the
number of cells which survive decreases. They have also found
that if the radiation is fractionated into smaller doses, with
one or more rest periods in between, fewer cells die. This is
because of self-repair mechanisms which repair the damage to
DNA[1][2] and other biomolecules such as proteins. These
mechanisms can be over expressed in cancer cells, so caution
should be used in using results for a cancer cell line to make
predictions for healthy cells if the cancer cell line is known
to be resistant to cytotoxic drugs such as cisplatin. The DNA
self repair processes in some organisms is exceptionally good;
for instance, the bacterium Deinococcus radiodurans can tolerate
a 15 000 Gy (1.5 MRad) dose.  In the graph below, called a cell
survival curve, the dose vs. surviving fraction have been drawn
for a hypothetical group of c