In breast cancer surgery, the radioisotope is injected to find the lymph node nearest the tumor, so it can be biopsied for signs of cancer, to determine whether more extensive surgery is needed. The alternative is to inject a dye, which sometimes does not let the surgeon find the node. Without the tool, Dr. Graham said, the quality of medical care is “dropping back into the 1960s.”
http://www.nytimes.com/2009/07/24/science/24isotope.html?_r=1&ref=us