Several epidemiological studies have recently been completed concerning the risk of thyroid cancer in relation to exposure to radioiodines, following the Chernobyl accident, fall-out from weapons testing or releases from nuclear installations. These studies have been carried out in Belarus, the Russian Federation, French Polynesia, the US (Hanford site) and the Marshall Islands, in populations with different genetic backgrounds and distributions of host and environmental risk factors, and most have collected information on a number of possible confounding or modifying factors.

A formal combined analysis of the studies of thyroid cancer was set-up to maximise the information that can be drawn concerning risks from iodine isotopes. The objectives of the analyses are:

1. a more precise evaluation of the risk of thyroid cancer related to exposure to I-131 in childhood and adolescence
2. comparing estimates of thyroid cancer risk in relation to exposure to iodine isotopes across studies in different settings and
3. a study of the role of environmental and host factors that may modify radiation induced thyroid cancer risk.

A total of about 700 cases with their more than 6.000 matched controls are included in the combined analyses; most of the subjects are from studies of the Chernobyl accident. Analyses are completed and soon will be submitted for publication.
As such, the study will maximise the information that can be drawn for radiation protection purposes from the separately carried out studies.
This study is supported by a grant from the Nuclear Fission Safety European Programme of the European Commission.