Lately everybody is talking about the Japanese nuclear accident, radiation and the risk of cancer. In the midst of one of these conversations, I was asked, “If radiation causes cancer, how come cancer is treated with radiation?” Another version is, “Since radiation breaks down DNA, which can cause cancer, how come we give radiation to treat cancer? Doesn’t it just break down more DNA?” That actually is a pretty good question.
Radiation therapy is commonly used to treat cancer. It is pretty effective for cancers that are localized (in one place). It is also very effective at treating more widespread cancers like Hodgkin’s Lymphoma.
For localized disease, it’s all in the focus. Radiation therapy can be focused like a laser flashlight beam. Very high levels of radiation are put in the area of the tumor and not much anywhere else. So any damage from radiation therapy is limited to the tumor – not exactly, of course, but pretty closely. Damaging tumor cells is the point, and we hardly need to worry about tumor cells becoming cancerous.
Some radiation treatments expose much more of the body to radiation. Treatments for Lymphoma are one example of this. People are given what would be concerning amounts of radiation if they got it working in a Japanese damaged nuclear facility. Here’s the interesting part: cancer cells and normal cells react differently to radiation. The way radiation damages cells is by causing breaks in DNA, the blueprint of life. It turns out that cancer cells are not very good at repairing their DNA. Normal cells are much better at successfully repairing the damaged DNA. So the damaged cancer cells die, and most of the damaged normal cells don’t.
If this sounds a bit imprecise, it is. Usually the difference between the cancer cell and the normal cell isn’t 100%. Most cancer cells don’t survive high-dose radiation, and most normal cells survive, repair themselves or die a clean death – just as long as they don’t turn into cancer.
This actually is the basis of cancer treatment of any kind. An important difference between the cancer and normal cells needs to be found and capitalized on.
But radiation is radiation. It damages DNA, and occasionally DNA is repaired badly – sometimes so badly it acquires something unpleasant like uncontrolled growth.
Studies do suggest to an increased risk of disease 20 or 30 years after radiation treatment. Cancer usually occurs in the middle years and later so many patients are cured of their cancer and are at the end of their natural life span before enough years have gone by to see any ill effects from the radiation treatment.
But ultimately, we worry about today and let tomorrow take care of itself. The prospect of not treating today’s cancer is so bleak that a future risk seems a small price to pay. Radiation, like so many other things in life, has its pros and cons.