Liver tumors are hard to treat with radiation because the liver moves every time you breathe. The purpose of this study is to test a new and possibly more accurate way of treating liver tumors. When a person is asleep under anesthesia, it is safe to stop breathing motion for a while. The liver will stop moving and radiation can be given to a liver tumor. The study is being done to see if radiation can be given to liver tumors safely and accurately in this way.