In radiation epidemiology many studies have been carried out to quantify the effects of external photon exposure, based on the Japanese A-bomb survivors, on patients with medical exposures and on nuclear workers. Today, the main issues to be considered in radiation protection are potential long-term health effects after exposure to other radiation types, like alpha-emitters. The general public daily inhales, at relatively low levels, alpha emitters that arise through domestic radon decay exposure. Various subgroups of nuclear workers are also exposed to alpha emitters during their occupational life. Only few studies are able to provide information on long term health effects after exposure to plutonium (Pu) and uranium (U) isotopes.

Objectives
The objective of the AlphaRisk project is to improve the quantification of long-term health risks, cancer and non cancer, associated to chronic internal contamination by alpha-emitters. It regrouped major studies in Europe that are able to consider chronic internal exposure in large populations and to evaluate associated long-term health effects. Advantage has been made of already existing European collaborations that worked successfully during previous EU contracts in order to strengthen expertise and increase statistical power for these low risk studies. Various complementary fields of expertise were involved: epidemiology, organ specific dosimetry, statistical modelling, and accounting for uncertainty in risk assessment. New studies were launched in the field of occupational exposure, by focusing on those workers for whom precise individual information on internal exposure has been registered during their occupational life. Collection and validation of these data made it possible to plan future large cohorts able to answer the question of a possible link between a disease and a specific exposure (example: uranium under different chemical forms). A casecontrol study realized during this program focused mainly on lung cancer and leukaemia risk.
The results of these studies were expressed as excess risk coefficients per unit of exposure or per organ dose and modelled in relation to time-dependent variables. The possibility of taking into account co-factors like occupational chemicals, tobacco, gender, age at exposure, and attained age was a major component of these joint analyses based on a large amount of data collected under the commonly shared study protocol.
It was possible to compare the calculated specific risk per organ dose with the more common risk per unit of exposure characterised by environmental measurements. The final objective of this large collaboration was the discussion of more or less sophisticated risk models as a tool for prediction of lifelong risks and for application to populations that differ from those directly involved in the present cohort or casecontrol studies. The comparison of these risk factors with those from populations exposed solely to external exposure was enhanced through this “organ dose approach”.