Artificial sources of radiation are commonly used in the manufacturing and service industries, research institutions and universities, and the nuclear power industry. As a result, workers can be exposed to artificial sources of radiation. There are also a significant number of workers, such as underground miners and aircrew, who are exposed to naturally occurring sources of radiation. This publication, prepared in collaboration with the International Labour Organization, and with reference to IAEA Safety Standards Series No. GSR Part 3 provides guidance for individuals and organizations on the assessment of prospective cancer risks due to occupational exposure to ionizing radiation for prevention purposes. It describes cancer risk assessment theory, models and methodologies, and offers practical examples of carrying out these assessments.