FIGURE 10B-3 Life-shortening data from Tables 1, 2, and 3 of Storer and others (1979). Plotted are the reciprocals of the mean life lengths of RFM female mice versus the dose of exposure, with different plotting symbols for acute (A) and chronically (C) exposed groups. The curves are the result of estimation of an LQ model for age-specific mortality rate fit to the 0–1.5 Gy dose range.

10B-4 is used as a “Bayesian prior distribution” in a Bayesian analysis. The resulting “posterior distribution” that results when this prior is multiplied by the LSS likelihood function is shown in Figure 10-3. The posterior density in the

TABLE 10B-1 Estimates of Linear and Quadratic Coefficients from Chromosome Aberration Induction Studies and the Implicit Curvatures

Human Cell Type

Radiation

α

β

θ

Lymphocytesa

Cobalt-60

0.015

0.06

4.0

Lymphocytesa

250 kV X-rays

0.04

0.06

1.5

Primary human fibroblastsb

Cesium-137 (acute)

0.059

0.029

0.5

Primary human fibroblastsb

Cesium-137 (chronic)

0.019

 

 

aFrom Lloyd and others (1992).

bFrom Cornforth and others (2002).

graph indicates the likely values of curvature and corresponding values of the LSS DDREF.

It should be evident that further study beyond that accomplished here could possibly lead to a better summarization of radiobiological information about curvature than provided in Figure 10B-4. Even a more thorough study, however, would similarly be obstructed by the subjectivity involved in the choice of dose range upon which LQ models are fit, by the inconsistency of animal experiment results, and by the difficulty in translating mouse results to human cancer rates.

The posterior density can be used directly to describe the uncertainty in LSS DDREF for the uncertainty analysis in Chapter 12. This distribution probably understates the uncertainty in knowledge of LSS DDREF, however, because of the various subjective choices involved. In an attempt to be more realistic about the state of knowledge of LSS DDREF, an inflated variance (of the distribution of the logarithm of LSS DDREF) is used in the uncertainty analysis.



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