Uses high-energy X-rays, electron beams, or radioactive isotopes to kill cancer cells without exceeding safe doses to normal tissue. It does this by ionization. Some cells die immediately after the radiation due to direct effect, but most die because the radiation damages the chromosomes and DNA so that they can no longer divide. There is limited usefulness for radiation in liver cancer patients. It is usually used in combination with surgery, if at all, and can treat the liver area after a tumor has been removed. Currently, radiation is used as a way to decrease the pain associated with larger liver masses and metastases.