Cancer risks from ionizing radiation--a good arena to study the influence of age at exposure There is much epidemiological data relating age-specific and organ-specific cancer incidence to the magnitude of exposure and age at which it occurred There is much animal data that is also age-specific, organ specific and for a variety of species and exposure patterns There are a plethora of cancer risk models that can be applied to these situations The time parameter in these models can be conveniently rescaled to relate to “biological processes” such as cell division There are no complications from metabolic activation or inactivation processes

For n-stage models with (differential) growth, analytic solutions are available that allow for a variety of exposure patterns, building from piece- wise linear patterns or integrating over point patterns. The versions we use are described in two unpublished papers “A Practical Approach to Using Epidemiological Data in Cancer Risk Assessment I: Risk Projections when there are Piece-wise Constant Exposure Histories” Robert L. Goble and Chao Chen, June 1997 “Insights from the Multistage Model into the Age- Dependence of Carcinogenic Effects” Weihsueh Chiu, December 2002

Here are some results from a very simple model: 5-Stages, no growth, and alternative effects of early life exposure on mutations at various stages Model # Mutation rate per.1% life Stage affected Lifetime absolute % cancers Age at flash exposure (%life) I --only stage 1 affected %6.2% (age 5 in an 80 yr life) II --only stage 4 affected %6.2% III --Pierce Mendelson.0013 for each stage all12.6%6.2% IV --smoking /radon analog.0045/ & 416.9%6.2% Back ground all10%lifetime