Monitoring Translocations by M-FISH and Three-color FISH Painting Techniques：A Study of Two Radiotherapy Patients

Purpose：To compare translocation rate using either M-FISH or FISH-3 in two patients treated for head and neck cancer, with a view to retrospective dosimetry. Materials and methods：Translocation analysis was performed on peripheral blood lymphocyte cultures from blood samples taken at different times during the radiotherapy (0 Gy, 12 Gy and 50 Gy) and a few months after the end of the treatment (follow-up). Results：Estimated translocation yield varied according to the FISH technique used. At 50 Gy and follow-up points, the translocation yields were higher with FISH-3 than with M-FISH. This difference can be attributed to three events. First, an increase in complex aberrations was observed for 50 Gy and follow-up points compared with 0 Gy and 12 Gy points. Second, at the end of treatment for patient A, involvement of chromosomes 2, 4, 12 in translocations was less than expected according to the Lucas formula. Third, a clone bearing a translocation involving a FISH-3 painted chromosome was detected. Conclusions：More translocations were detected with M-FISH than with FISH-3, and so M-FISH is expected to improve the accuracy of chromosome aberration analyses in some situations.