world, including Japan. Breast cancer, thyroid cancer, and leukemia were evaluated in the BEIR V (NRC 1990) report.

As far as feasible, the effects of both external and internal (¹³¹I) low-LET radiation exposures are considered separately. The focus on low-LET irradiation is related to the goal of BEIR VII to investigate the magnitude of risk from these radiation types. Although the focus of this report is the effects of low doses (i.e., doses less than 100 mGy), results of medium- and high-dose studies are also reviewed because they provide important insights into modifiers of radiation risks that cannot, at present, be studied in populations with lower-dose medical exposures.

The information presented in the previous section of this chapter was used to identify the studies that are informative for radiation risk estimation and have provided estimates of risk per gray in a comparable fashion (either as ERR or as EAR). The estimates have been taken from the original publications. When such estimates were not available in the original study reports, these studies have not been included in this section, with the exception of the study of breast cancer in cervical cancer survivors (for which risk estimates were taken as derived by UNSCEAR 2000). No estimation was attempted by the committee because there is considerable uncertainty in deriving risk estimates based on only an average dose in populations with dose distributions that are often skewed and include subjects with very high, cell-killing doses.

The estimates from these studies are summarized in Tables 7-2 to 7-6 and Figures 7-1 to 7-6. In the following sections, differences and similarities among risk estimates are discussed, and conclusions are drawn, where possible, about radiation risks for each of the cancer sites of interest. Since the conditions of exposure, the characteristics of the study populations, and the extent and quality of the dosimetry and follow-up differ widely, the risk estimates derived for individual studies are not strictly comparable. They do, however, illustrate the range and significance of estimates obtained and provide some indication of the influence of the study-specific factors involved.

Lung cancer is the leading cause of cancer mortality in industrialized countries, and its incidence is rising in many developing countries. Cigarette smoking is accepted to be the primary cause of lung cancer. Also, ionizing radiation