logic studies are also used for estimating risks to specific exposed populations, such as underground miners exposed to radon (NRC, 1999) and populations exposed to iodine-131 (131I) (UNSCEAR, 2000).

The International Commission on Radiological Protection (ICRP) and the National Council on Radiation Protection and Measurements (NCRP) are moving to use tumor incidence, rather than mortality, in their revised cancer risk estimates. Using tumor-incidence data for developing risk estimates provides an additional useful measure of risk because morbidity entails health, emotional, and financial costs to the individual and society.

In this chapter, we consider and present the evidence from new or updated epidemiologic studies, radiation-biology advances, or dosimetry approaches that could result in significant changes in the risk estimates for human cancer induced by ionizing-radiation exposure. This chapter brings together information that could influence compensation for diseases currently covered by RECA legislation. In Chapter 7, we discuss additional diseases brought to our attention by members of the public at a series of hearings held in response to community invitations with a view to whether eligibility for coverage should be extended thereto. The following sections discuss what is new in those fields of study.

RECENT DEVELOPMENTS IN RADIATION EPIDEMIOLOGY

Epidemiologic studies of the Japanese survivors of the atomic bombs and of other populations exposed to radiation medically, occupationally, or accidentally have characterized the long-term health effects of radiation (see Chapter 3). Risks estimates for radiogenic cancers and nonmalignant diseases now compensable under RECA come primarily from epidemiologic studies of uranium and other underground miners exposed to radon and from studies of the atomic-bomb survivors. The mining populations were exposed primarily to radon internally while the atomic-bomb survivors were exposed primarily to external gamma rays. Risk estimates for thyroid cancer also come from populations exposed to external x and gamma rays, and internally to radioiodine. Studies of worker populations exposed to low or very low doses of low LET radiations over long periods provide radiogenic-cancer risk estimates with which the more precise estimates obtained from the atomic-bomb survivors can be compared to evaluate their applicability to populations chronically exposed to low radiation levels. Extensive and detailed reviews of those studies have been reported previously (NRC, 1990, 1998; 1999; ICRP, 1991; UNSCEAR, 1993, 2000; IARC, 2000; 2001).

A comprehensive reassessment of risk estimates is included in a companion, forthcoming report from the National Research Council Committee on Biological Effects of Ionizing Radiation (BEIR) specifically, the Committee on Health Risks from Exposure to Low Levels of Ionizing Radiation (BEIR VII).



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