combined at radiation dose levels greater than about 200 mSv (31). 3.3.2.1 Radiogenic Tumors Although all tissues are considered to be susceptible to radiogenic tumorigenesis, some tumors have been shown to be more strongly associated with prior radiation exposure than others. Based on current epidemiologic data, tumor types most strongly associated with exposure to radiation are benign thyroid nodules, all types of leukemia, except the chronic lymphocytic type, and cancers of the lung, female breast and thyroid. Exposure to radiation from certain internally deposited radionuclides also has been associated unequivocally with malignancies of target organ tissues, significantly thyroid (radioactive iodines), lung (radon) and bone (radium), and leukemia and lungin the case of injected Thorotrast. Theradiogenicity of malignancies of the head and neck (other than thyroid), digestive and genito-urinary systems, brain and the central nervous system, and skin appears to be weaker than is the case for the malignancies listed above; and it is equivocal or unidentified for certain site-specific malignancies within these organ systems, such as Hodgkins lymphomaand cancers of the uterus and prostate (2). Although there have been some suggestions to the contrary, there is to date no strong evidence of increased cancer rates among children or adults who were exposed to radiation in utero (26). 3.3.2.2 Latent Periods and Duration of Increased Risks Based on the epidemiologic data, the minimum latent periods (interval between exposure and diagnosis) for. radiation-induced leukemia and solid cancers are generally accepted to be 2-5 years, and 10 years, respectively. The increased risk of radiogenic leukemia appears to decrease almost to the natural baseline rate for the control population 25-30 years postexposure. However, the risk for most solid cancers remains substantially elevated for at least 40 years post-exposure (2). 12 JUL 2019