Intercomparison of Translocation and Dicentric Frequencies Between Laboratories in a Follow-up of the Radiological Accident in Estonia

Purpose: To perform an interlaboratory comparison of FISH chromosome painting and to study the time-course of translocations and dicentrics in three accident victims exposed to radiation. Also, to use the data in the validation of the FISH technique as a retrospective dosimeter.

Materials And Methods: Twelve blood samples were collected during 4 years from three subjects exposed to radiation in an accident in Estonia in 1994 involving gamma-radiation from a 137Cs source. Two of the subjects were exposed during approximately 7 h, both receiving a protracted dose of about 1 Gy and also localized exposure. The third subject received a protracted whole-body dose of 2.7 Gy during 4 weeks as well as a short-term partial-body dose. Preparations from 48-h metaphase cultures were painted by the FISH technique using routine methods and probe cocktails in four laboratories. Samples from each subject were analysed in two different laboratories that used different combinations of whole chromosome probes. The PAINT nomenclature was applied when recording chromosome aberrations.

Results: The intercomparison of FISH analysis data showed reasonable similarities between laboratories, the largest discrepancy being 21% in the frequency of two-way translocations in subject 3. Half-time calculations, based on combined data sets from two laboratories, showed that dicentrics decreased rapidly with half-times of approximately 2 years. In all cases, the initial dicentric yields were lower than the initial translocation yields. During the 4-year follow-up, the frequencies of all translocations in cells containing only simple rearrangements fell on average to about 65% of their initial value. Two-way translocations were slightly more persistent than all translocations. The average half-time was about 8 years for two-way translocations and around 6 years for all translocations. Cells containing complex rearrangements were few in number and they disappeared with time. In general, the inclusion of complex cells caused a more rapid fall in aberration yield.

Conclusions: In general, the results imply that relatively consistent scoring data were obtained with different chromosome painting protocols. They also support the idea that the reduction of translocations with time is associated with partial-body irradiation.