It can come from radioactive substances and special machines. There are many different levels of radiation energy. We have all been exposed to some low levels of radiation energy, such as radiation from the sun or radiation used to make a chest x-ray or mammogram. When radiation energy is used at high levels, it can treat cancer and other illnesses. The use of high-energy rays or particles to treat a disease is called radiation therapy .
Cancer is a tumor, or an overgrowth of abnormal cells.
These cells grow by multiplying or dividing to rapidly make new tumor cells. The ability to multiply without limits, grow quickly, and grow into surrounding normal tissues makes cancer cells different from normal cells. There are many different types of cancer. Each type of cancer is unique in how it grows and how it responds to treatment. One way to stop the cancer from growing is to interfere with the cancer cell s ability to multiply.