How can radiation both be a cause of cancer and also be used to treat cancer?
The “current wisdom” is that cancer begins with a single cell having abnormal genetic instructions. Over time, it (or one of its descendant cells) acquires additional injuries. Finally, a cell’s abnormal instructions cause it to do abnormal things — such as dividing too often, or forming a tumor, or migrating from its appropriate location to live and divide elsewhere in the body (metastasis). These cancerous activities are done by living cells, whose abnormalities can be caused by radiation. When radiation is used to treat cancer, it is used in very high doses which do enough damage to kill cells. Dead cells cannot behave like cancer. It is very difficult to give radiation only to cancer cells, without giving both high and low doses of radiation to healthy cells in the neighborhood. Methods in radiation therapy are improving with time.
