There were negative associations between ionizing radiation and liver cancer in studies of radium dial painters, radiologists, underground miners, nuclear workers, uranium processors, and Mayak workers. There was strong evidence that Thorotrast (Th-232) caused liver cancer when used as a radiographic contrast agent between 1928 and 1955. [Boice, p. 261, 271] Hepatocellular carcinomas (HCC) comprise about 75% to 90% of liver cancers. "Eighty to 95% of HCCs are associated with chronic infection of hepatocytes with either of two viruses, hepatitis B virus (HBV) or hepatitis C virus (HCV)." [Schottenfeld, p. 763] See "Angiosarcoma of the liver."