Dose fractionation effects are utilised in the treatment of cancer with radiation therapy. When the total dose of radiation is divided into several, smaller doses over a period of several days, there are fewer toxic effects on healthy cells. This maximizes the effect of radiation on cancer and minimizes the negative side effects. A typical fractionation scheme divides the dose into 30 units delivered every weekday over six weeks. Hypofractionation is a treatment regimen that delivers higher doses of radiation in fewer visits, which tends to lower the effects of accelerated tumor growth that typically occurs during the later stages of radiotherapy. Hyperfractionation is dividing the same total dose into more deliveries, so that treatments are given more than once a day. Hyperfractionated radiation therapy is given over the same period of time as standard radiation therapy. Accelerated fractionation has also been investigated.
Background
s 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 dose. to cause cell death. The blue line is for cells which were not given a chance to recover; the red line is for cells which were allowed to stand for a time and recover. In the graph to the right, called a cell survival curve, the dose vs. surviving fraction have been drawn for a hypothetical group of cells with and without a rest time for the cells to recover. Other than the recovery time partway through the irradiation, the cells would have been treated identically. The human body contains many types of cells, and the human can be killed by the loss of a single type of cell in a vital organ. For many short-term radiation deaths due to what is commonly known as radiation sickness, it is the loss of bone marrow cells, and the loss of other cells in the wall of the intestines, that is fatal.
Fractionation effects are utilised in the treatment of cancer with radiation therapy. When the total dose of radiation is divided into several, smaller doses over a period of several days, there are fewer toxic effects on healthy cells. This maximizes the effect of radiation on cancer and minimizes the negative side effects. A typical fractionation scheme divides the dose into 30 units delivered every weekday over six weeks. Hypofractionation is a treatment regimen that delivers higher doses of radiation in fewer visits. The logic behind this treatment is that applying greater amounts of radiation works to lower the effects of accelerated tumor growth that typically occurs during the later stages of radiotherapy. Hyperfractionation is dividing the same total dose into more deliveries. Treatments are given more than once a day. Hyperfractionated radiation therapy is given over the same period of time as standard radiation therapy. Accelerated fractionation has also been investigated.
