Fallout cancers estimated in the CDC feasibility report

August 2001

Q: What are the health effects from this exposure?

A: At these low-dose levels the most important health effect is likely to be cancer.While some non-cancer diseases have been reported as late effects of radiation, more fundamental research is needed to clarify the biological mechanisms by which low-dose,protracted radiation exposure causes these diseases. Based on the dose data available inthis feasibility assessment, the most likely non-cancer health outcomes that may affect the American people are those involving the thyroid gland. Preliminary estimates of dose from fallout radiation indicate that the internal organ-specific dose to the thyroid is muchhigher than the dose to other organs/tissue evaluated. Internal and external exposures tofallout radiation are unlikely to result in an increase in other non-neoplastic diseases at the currently estimated dose levels. However, it is possible that select individuals may have much greater sensitivity to radiation than has been found on average.

Q: How many cancers could occur as a result of fallout exposure?

A: Based on an average external dose to the American public of 1.2 mGy, we estimate that about 11,000 extra deaths from all cancers may occur among the residents of the United States who were alive at any time during the years 1951-2000. These 11,000 deaths would be spread out over the period extending from the 1950s into the 21st century, and would be in addition to the far larger number of cancer deaths that occur every year in the United States; for example, about 500,000 cancer deaths occurred in 1990 and about 40 million cancer deaths might be predicted to occur over a 75-year period. About 10% of these additional 11,000 cancer deaths from external exposure may be predicted to be from leukemia.

Internal exposure to radionuclides in fallout may also result in additional cancers in specific organs and tissues of the body. For example, an additional 550 deaths from leukemia may occur among the people who lived in the United States anytime during andincluding the years 1951-2000 as a result of internal exposure to the red bone marrowfrom fallout radionuclides. And, previous estimates by NCI predict between 11,300 and 212,000 thyroid cancer cases may be expected to occur among the United States population from exposure of the thyroid gland to Iodine-131 from the Nevada Test Site. Of those cases, we would expect that the number of deaths from thyroid cancer would be between about 1,000 and 21,000. Consideration of global fallout produced at other locations around the world would likely increase these thyroid cancer estimates by about 10%.

Q: Why are you providing a range of numbers instead of one number for an estimate of thyroid cancers? Why are you not providing a range of numbers for all cancers and leukemia, too?

A: Because we cannot measure actual organ doses in people nor count the actual number of cancers that result from exposure to radioactive materials from nuclear weapons testing fallout, all estimates of risk must be made using mathematical models. Because components of these mathematical models are uncertain, all estimates of risk are inherently uncertain. The estimates of thyroid cancer cases presented in the Progress Report to Congress are based on previous work conducted by NCI in which an attempt was made to account for some sources of uncertainty (specifically, statistical uncertainty in the risk coefficient and uncertainty in the dose). Thus, a range of possible values is presented. The Progress Report to Congress presents results for all cancers and leukemia for illustrative purposes only, and these results may contain considerable error. The draft Technical Report will include a crude quantitative estimate of the uncertainty associated with the estimates of all cancers, and it will discuss the concepts of uncertainty in more detail.