Dose fractionation

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 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.