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Lymphoma and Pets
Does Radiation Treat Cancer or Cause Cancer?
The short answer: both.
The Long Answer
Let's begin with a simple definition of radiation: Radiation is the energy emitted from an energy source. That energy source can be the sun, power lines, your television, radio waves - anything that emits energy.
Radiation, in that simple definition, is everywhere. When you turn on an AM/FM radio, it's not as though the radio went looking for the radiating signal. Instead, the radiating signal is already there whether your radio is on or not. That's how pervasive radiation is in the world.
When Radiation is a Health Issue
There are two forms of radiation: ionizing and non-ionizing radiation. The difference between the two is simple:
To ionize something means to remove electrons from atoms or molecules, so ionizing radiation has sufficient energy to ionize things and break chemical bonds. In order to be ionizing radiation, the radiation has to be high-frequency (high energy), like gamma rays, X-rays and sometimes ultraviolet rays.
Non-ionizing radiation, therefore, refers to any radiation without enough energy to cause ionization. This includes radiation on the electromagnetic frequency below ultraviolet radiation, including visible light, infrared, microwaves, and radio waves. It is believed that even prolonged exposure to non-ionizing radiation will not induce health problems, although this is a contentious area of scientific debate.
There are two categories of health effects from radiation exposure, and they depend on the amount of radiation you're exposed to and the amount of time you're exposed to it. These categories are called stochastic and non-stochastic effects.
Stochastic effects of radiation are the instances when radiation causes cancer.
These effects are associated with long-term, chronic exposure to radiation. As the Environmental Protection Agency reports, in stochastic health effects, "increased levels of [radiation] exposure make these health effects more likely to occur, but do not influence the type or severity of the effect."
When cancer occurs, the ionizing forms of radiation are powerful enough to harm human tissue and to change the DNA in cells. It does this by its ability to break chemical bonds. When that tissue is damaged by ionizing radiation, the body tries to repair the damage. Sometimes it succeeds; sometimes it doesn't. The non-repairable damage in the DNA can lead to mutations that survive and prosper as cancer. Or, sometimes, during the process of repair, something goes awry and causes a cancer to develop.
In any event, the risk of cancer becomes more likely the more a person is exposed to this kind of radiation. For this reason, doctors try to limit the number of X-rays, CT scans and other radiology procedures a patient receives because, over a lifetime, they can add up and boost one's risk of developing cancer.
Non-stochastic effects of radiation include, among other things, the instances when radiation treats cancer.
Instead of long-term, low-level and chronic exposure to radiation, non-stochastic effects refer to exposure to high levels of radiation in a short period of time. For example, when the nuclear reactor at Chernobyl exploded, a number of men were sent into the core to try and clean it up. These men suffered burns, nausea, weakness, hair loss and radiation sickness. After being exposed to incredibly high levels of radiation in an incredibly short period of time, the men died within days or weeks of exposure.
Coincidentally, when radiation is used as therapy to treat cancer, patients are exposed to short, high-energy bursts of radiation and often suffer temporary radiation sickness. This kind of high-level radiation kills cells in the body very, very quickly - in a fraction of a second. If exposure becomes prolonged and the exposed areas include healthy cells, then it can become cancer-causing, a process that can take decades to develop.
For this reason, researchers are always working on ways to limit the exposure of healthy tissue to radiation therapy and try to focus as much of it on the cancerous cells as possible so that only the DNA in those cells is damaged to the point of cell death.
Cancer Types and Ionizing Radiation
Ionizing radiation can cause cancer in whichever part of the body is exposed to it, but some cancer types seem more common than others. They include leukemia and cancers of the bone marrow, as well as thyroid cancer. Other cancers associated with exposure include lung cancer, skin cancer, breast cancer and stomach cancer. For instance, some studies have shown that women with Hodgkin's lymphoma who are treated with chest radiation are at higher risk of developing breast cancer when they are older.
You can read more about secondary cancers caused by cancer treatment at the American Cancer Society.