Commentary and Review Series 3-89
Calculating excess lifetime risk in relative risk models
Vaeth M, Pierce DAEnviron Health Perspect 87:83-94, 1990
Summary
When assessing the impact of radiation exposure, it is common practice to present the final conclusions in terms of excess lifetime cancer risk in a population exposed to a given dose. The present investigation was mainly a methodological study focusing on some of the major issues and uncertainties involved in the calculation of such excess lifetime risks and related risk projection methods. The age-constant relative risk model used in recent analyses of the cancer mortality observed in the follow-up of the cohort of atomic bomb survivors in Hiroshima and Nagasaki was used to describe the effect of radiation exposure on cancer mortality. In this type of model, the excess relative risk is constant in age-at-risk, but depends on the age-at-exposure.
Calculation of excess lifetime risks usually requires rather complicated lifetable computations. Here a simple approximation to the excess lifetime risk has been proposed and the validity of the approximation for low levels of exposure has been justified empirically as well as theoretically. This approximation will provide important guidance in understanding the influence of the various factors involved in risk projections. Among the further topics considered were: the influence of a latent period, the additional problems involved in calculations of site-specific excess lifetime cancer risks, the consequences of a leveling off or a plateau in the excess relative risk, and the uncertainties involved in transferring results from one population to another.
The main part of this study relates to a situation characterized by a single, instantaneous exposure, but a brief discussion of the problem for a continuous exposure at a low dose rate is also given.
When assessing the impact of radiation exposure, it is common practice to present the final conclusions in terms of excess lifetime cancer risk in a population exposed to a given dose. The present investigation was mainly a methodological study focusing on some of the major issues and uncertainties involved in the calculation of such excess lifetime risks and related risk projection methods. The age-constant relative risk model used in recent analyses of the cancer mortality observed in the follow-up of the cohort of atomic bomb survivors in Hiroshima and Nagasaki was used to describe the effect of radiation exposure on cancer mortality. In this type of model, the excess relative risk is constant in age-at-risk, but depends on the age-at-exposure.
Calculation of excess lifetime risks usually requires rather complicated lifetable computations. Here a simple approximation to the excess lifetime risk has been proposed and the validity of the approximation for low levels of exposure has been justified empirically as well as theoretically. This approximation will provide important guidance in understanding the influence of the various factors involved in risk projections. Among the further topics considered were: the influence of a latent period, the additional problems involved in calculations of site-specific excess lifetime cancer risks, the consequences of a leveling off or a plateau in the excess relative risk, and the uncertainties involved in transferring results from one population to another.
The main part of this study relates to a situation characterized by a single, instantaneous exposure, but a brief discussion of the problem for a continuous exposure at a low dose rate is also given.