Good dosimetry is essential to estimate with reasonable accuracy the radiation risks resulting from the Chornobyl accident. The tasks that were assigned to the REB dosimetrists in the framework of two epidemiological studies (Thyroid Diseases in Young Persons in Belarus and Ukraine after the Chernobyl Accident and Study of Leukemia Risk in Chernobyl Ukrainian Clean-up Workers) include:

• The development of a method of thyroid dose estimation for children exposed to radiation after the Chornobyl accident.
• The application of that method to estimate individual thyroid doses for all Belarusian and Ukrainian cohort members.
• The development of a method of thyroid dose estimation for children exposed in utero to radiation after the Chornobyl accident.
• The application of that method to estimate the thyroid doses for all Ukrainian study subjects exposed in utero.
• The development of a method of bone-marrow dose estimation for the Chernobyl clean-up workers.
• The application of that method to estimate individual bone-marrow doses for a cohort of Ukrainian clean-up workers

More specifically, the aims of the REB dosimetrists in the thyroid studies are : (1) to provide accurate individual I-131 thyroid doses for the approximately 25,000 subjects included in the Belarusian and Ukrainian cohorts; (2) to assess the uncertainties attached to the individual I-131 thyroid dose estimates; and (3) to evaluate the usually minor contributions to the thyroid dose resulting from the intake of short-lived radioiodines (I-133 and I-135) and radiotelluriums (Te-131m and Te-132), the intake of the long-lived radiocesiums (Cs-134 and Cs-137), and external irradiation arising from the deposition of radionuclides on the ground and other materials, and (4) to provide thyroid dose estimates to persons exposed in utero.

In the leukemia project, the aims of the REB dosimetrists are: (1) to provide accurate individual bone-marrow doses for all cases and controls using new and existing information and models; and (2) to assess the uncertainties attached to the bone-marrow dose estimates.

The REB dosimetrists also are collaborating with the International Agency for Research on Cancer (IARC) to develop common methods of dose estimation for the Chornobyl studies and were actively involved in the activities of the United Nations Chernobyl Forum.