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Dose fractionation effects are utilised in the treatment of
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 (3 to 30 days after exposure), it is the loss of bone marrow cells (which produce
cancer
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
with radiation therapy
Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation, generally provided as part of cancer treatment to control or kill malignant cells and normally delivered by a linear accelerator. Radi ...
. When the total dose of radiation is divided into several, smaller doses over a period of several days, there are fewer toxic
Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subs ...
effects on healthy cells. This maximizes the effect of radiation on cancer and minimizes the negative side effects
In medicine, a side effect is an effect, whether therapeutic or adverse, that is secondary to the one intended; although the term is predominantly employed to describe adverse effects, it can also apply to beneficial, but unintended, consequence ...
. 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 (days or weeks) as standard radiation therapy. Accelerated fractionation (two deliveries per day and/or deliveries on weekends as well) has also been investigated.
Background
Experiment
An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into Causality, cause-and-effect by demonstrating what outcome oc ...
s in radiation biology
Radiobiology (also known as radiation biology, and uncommonly as actinobiology) is a field of clinical and basic medical sciences that involves the study of the action of ionizing radiation on living things, especially health effects of radiation. ...
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
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
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
Cisplatin is a chemotherapy medication used to treat a number of cancers. These include testicular cancer, ovarian cancer, cervical cancer, breast cancer, bladder cancer, head and neck cancer, esophageal cancer, lung cancer, mesothelioma, ...
. The DNA self repair processes in some organisms is exceptionally good; for instance, the bacterium Deinococcus radiodurans
''Deinococcus radiodurans'' is an extremophilic bacterium and one of the most radiation-resistant organisms known. It can survive cold, dehydration, vacuum, and acid, and therefore is known as a polyextremophile. It has been listed as the world' ...
can tolerate a 15 000 Gy (1.5 MRad) dose.
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 (3 to 30 days after exposure), it is the loss of bone marrow cells (which produce blood cells
A blood cell, also called a hematopoietic cell, hemocyte, or hematocyte, is a cell produced through hematopoiesis and found mainly in the blood. Major types of blood cells include red blood cells (erythrocytes), white blood cells (leukocytes), a ...
), and the loss of other cells in the wall of the intestines
The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...
, that is fatal.
Radiation fractionation as cancer treatment
Fractionation effects are utilised in the treatment ofcancer
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
with radiation therapy
Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation, generally provided as part of cancer treatment to control or kill malignant cells and normally delivered by a linear accelerator. Radi ...
. When the total dose of radiation is divided into several, smaller doses over a period of several days, there are fewer toxic
Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subs ...
effects on healthy cells. This maximizes the effect of radiation on cancer and minimizes the negative side effects
In medicine, a side effect is an effect, whether therapeutic or adverse, that is secondary to the one intended; although the term is predominantly employed to describe adverse effects, it can also apply to beneficial, but unintended, consequence ...
. 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 (days or weeks) as standard radiation therapy.
Accelerated fractionation (two deliveries per day and/or deliveries on weekends as well) has also been investigated.
References
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