The calculations (see attached Excel spreadsheet)

Column 1 identifies the exposure ages considered. The first year of life was treated separately and older ages were grouped: 1-4, 5-9, 10-14, and 15-19. Exposure at ages older than 20 was ignored because there is little or no evidence of an excess cancer risk associated with exposure in adult life even to gamma and x-ray irradiation. Columns 2 and 3 give the estimated number of persons in the 1952 population of the US, by age and sex, as interpolated from 1950 and 1960 census numbers. The total number exposed at ages 0-19 also includes persons born in 1953, 1954, etc., but the entry into the population of newborn persons is largely compensated by the loss of persons reaching age 20 in the same years. With a linear dose-response model and lifetime excess risk, error introduced by acting as if the population 0-19 years of age in 1952 received all the dose that was actually received by those who were 0-19 years old during any part of the above-ground testing period is relatively unimportant.

Column 4 gives age-specific average thyroid doses in rad corresponding to the assumed average dose of 2 rad (0.02 Gy), based on information provided by André Bouville (this is why the first year of life was separated from the next four). As you know, thyroid doses to children are larger than those for adults because of smaller gland size, higher milk intake, and higher metabolism.

Column 5 gives the age-specific, linear dose-response coefficients for x ray and gamma ray, derived from Ron et al. (1995). Their overall coefficient for excess relative risk (ERR) at 1 rad was 0.077. They also did analyses suggesting that the ERR decreases by a factor of 2 for each successive 5-year interval of age at exposure, over the range 0-14 years of age. I derived the values in column 5 from the Ron et al. analysis, and extended the 2-fold reduction rule to 15-19 years at exposure. In each subsection, the age-specific coefficients have been multiplied by the specified RBE value.

Columns 6 and 7 are the estimated lifetime excess thyroid cancer rates for males and females, computed by multiplying the product of columns 4 and 5 by 0.25% for males and 0.64% for females, respectively; these percentages are the SEER (1973-1992) report's estimated lifetime thyroid cancer rates for men and women. The 1973-1994 SEER volume is now out, and gives 0.27% for males and 0.66% for females. Use of the new values would increase the total by about 4%.

Columns 8 and 9 were obtained by multiplying columns 2 and 3 by columns 6 and 7, respectively, and column 10 is the sum of columns 8 and 9. One implication of column 10 is that 75% of all the excess risk is estimated to result from exposure during the first 5 years of life.

The calculations are repeated for RBE values of 1.0, 0.66, 0.3, and 0.1.



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